Back in Alpha, there was a well-known cycle of instants with a casting cost of one and they all gave you three point of something. Healing Salve is much derided (rightly so) as being very weak, while Giant Growth still sees some constructed play when legal in Standard, Dark Ritual is now way too powerful to see its way back into Standard (the effect is now in red, pulled back into sorcery territory and the rate you get is much worse), and Lightning Strike is a cornerstone of the format in both Modern and Legacy. These were all common. And then there was Ancestral Recall. One mana, draw three cards. Jury is still out on whether Recall or the iconic Black Lotus is the most powerful card in the game. Recall was also (rightfully) rare.
Since then drawing spells have been nerfed. Recall just went into every deck that could possibly play it. If a deck couldn’t play it, you were probably doing something wrong. Since then things have become more complicated.
Divination is the current baseline. It has made its way into a variety of control decks in the recent years. Mostly as a way to dig deeper into the deck to find the real ways to get card advantage. Right now that target is mostly Dig Through Time. In the last Standard it was Sphinx.
When should you use this card? It requires some planning. The raw card advantage gained from a Divination is actually pretty low. If you are playing 24 lands in your deck (and most control decks are playing more), 40% of your draws are lands. That means you are exchanging (on average) your spell for 1.2 spells and using mana to do it.
So, in most decks this card advantage and the loss of your third turn when your opponent is generally going to be playing something strong (such as Goblin Rabblemaster, Brimaz, King of Oreskos, Anafenza, the Foremost, or ramping into Siege Rhino) is going to be too much of an investment for such a small benefit.
On the other hand, if you need to make land drops, and need to dig for something else (such as sweepers or just removal), a set of Divinations essentially make the size of your deck 52 instead of 60 (not quite this straightforward, but close enough). This gives the deck better consistency.
Better than Divination
In contrast, the black variant Sign in Blood is cheaper in mana, so it can be played in decks with less lands, thus giving us a better rate in spells, and Read the Bones includes card selection, so it can be used to dig even deeper into the deck, or have a better rate in spells drawn then its blue counterpart. Of course, in each of these cases there is a cost in life. Whether its worth it depends on your deck and the metagame.
Where as black will generally change other resources for cards, red has a very different approach.
Voice is not true card advantage, but it has the same function of filtering through your deck as Divination, but is cheaper. Since you often have cards you can freely discard, you might not lose much card quality. It might be situational, but so is Act on Impulse. Act on Impulse relies on you having plenty of mana available. Sure, you can probably hit a land drop with it if you are desperate, but that’s not the kind of situation you won’t to be in, so you can’t really build your deck to get there.
Of those two, Voice is seeing some constructed play. Not much as of yet, but I imagine that will change, as it can be a great card in the right deck. For example, it might work in many decks relying on Prowess.
But of course, there’s always blue, and blue is the master of card draw.
Recently, Treasure Cruise has been proving this basic fact. According to Magic TV (by Channel Fireball) its the best card in Modern currently, only narrowly edging out Dig Through Time. Basically Treasure Cruise is just a nerfed Ancestral Recall, but if we look back at all the other nerfed versions of it, we’ll see that it hasn’t gone that well in the past either (see Ancestral Vision, Brainstorm for reference).
The thing about Treasure Cruise is that you can’t cast it early, but when you can, its going to be very cheap with a very good return on the investment. I’ve heard stories about very untuned decks in Modern that simply splash for Treasure Cruise as a fourth color. Its simply that strong if you can hinder your opponents game long enough to be able to cast it. Here, things like fetches and cantrips definitely help.
Once again, back in the day, Alpha had Jayemdae Tome. It has seen plenty of printings, most recently in M13. It isn’t used much, as its usually much too expensive to use. This hasn’t always been so. Even back in the days of Ancestral Recall, The Deck, the original blue-white control deck (although it did splash for both black – Demonic Tutor – and red – Red Elemental Blast, in the main deck) had one Tome in the main and another in the sideboard (it also had one Library of Alexandria and one Braingeyser in the main, giving the deck multiple subtly different ways to outdraw the opponent).
Although activating the Tome is quite expensive, apparently Brian Weissman thought it was still good enough in this deck filled with Power Nine and other insanely strong cards from the early days of Magic, like Moat and Sol Ring. After all, this was truly The Deck in its day.
But the king was Necropotence.
Seemed quite innocuous back in the day. I remember people thinking it was a junk rare and thinking about how to give it to their opponents. After all, not being able to draw cards is a huge drawback, right? But this was 1995. People couldn’t evaluate cards properly back then. Sure it cost you life as well as draws, but what you gain instead is also huge. It took about a year before the card rose into prominence at Pro Tour #1, but after that, the summer of 1996 was known as the Black Summer, as monoblack decks dominated.
Actually, It wouldn’t even been such a huge thing without enablers, the most important of which was Dark Ritual. You wouldn’t mind taking a mulligan or two just to be able to get that pair and use a couple of life to make up for the difference. Other enablers included Hypnotic Specter and Hymn to Tourach, which let you devastate your opponent while you drew all those cards yourself, and Nevinyrral's Disk to reset the board after you’ve forced your opponent to play out their hand with your discard and used up your life with your ‘Potence.
Card draw doesn’t live in a void. There are other resources you have to use to gain the advantage and good players will be able to abuse that resource usage. In case of ‘Potence, Black Vise kept it in check until it was restricted, and after that so called Turbo-Stasis decks rose into prominence, which could effectively lock out the ‘Potence players pretty fast.
More recently, Underworld Connections and to some extent Erebos, God of the Dead have been in a similar role. You pay a card and some mana each turn (and life) for the benefit of being able to draw a card each turn. With the investment in mind, you need to be able to have enough time to have your investment pay off.
These cards were popular in the Black Devotion decks, as well as some other decks, such some versions of Jund Monsters. With quite a few lands in the deck, you need to be able to regain the inherent spell decifit somehow. For just that, you use card draw (as well as sweepers and other tools).
These days, the decks with a good early game, are really, really fast and card draw is designed and costed in such a way that you can’t get an early advantage and be able to use it, except in slow matchups. On the other hand, if the fast deck can’t take you out in the early turns, and you can gain card advantage with whatever tools you have, you will eventually win.
Currently, there doesn’t seem to be any consistent sources of card advantage, with the exception of Courser of Kruphix, which doesn’t really let you draw cards, but will provide advantage through filtering lands off the top of your deck. I’m sure there will be something, or Erebos will make its return (or Pain Seer will finally have its day, although I’m not sure about that).
There have been plenty of these cards in the past, and there will be plenty more to come. You’ll just need to be able to evaluate them.
Like most games, MtG is about resource management and luck. Of those resources, the easiest to leverage into a win, is card advantage. (Well, not quite, as people do generally like to start, so I guess the easiest is tempo, but card advantage is easier to talk about.)
With cards that give you card advantage, you are exchanging resources for resources. Mostly cards and mana. When is it beneficial to use such effect? Usually when they cost resources you are ready and able to forfeit, and you can bypass the manacost, the card draw will suddenly become very tempting. Think Dark Confidant or the previously mentioned Treasure Cruise (which has largely made the Dark Confidant redundant). They give you card advantage for life or your graveyard respectively. That’s usually a trade you are willing to make.
Just remember that even if card advantage is great, it won’t always just let you win. If you overload your deck with card advantage, you are digging into the portion of the deck that has the cards you are trying to draw into. Remember the Divination from before? If you play it in a deck with 26 lands (pretty common for a control deck), you’ll draw just 1.133 spells for each Divination. Alone that’s not good enough. There needs to be a reason for you to do this.
Of course, limited is a wholly different animal. There digging to your bombs might be a very important concern.