I’ve come across plenty of situations where you want to kill your own creature for one reason or another. Its just that since this is pretty lateral thinking, you might not always identify these situations. So, I’m here to help…
My opponent was at one life, but was quickly stabilizing the board. However, I had an out: [scryfall]Tormented Hero[/scryfall] + [scryfall]Ultimate Price[/scryfall] means draining one life. Sadly I missed this one. The funny thing is, I identified the possibility of this situation the week before, but just forgot about it.
I was playing my usual Suicide Black deck and the opponent played a [scryfall]Blood Baron of Vizkopa[/scryfall]. Usually that’s lights out, right? However, I did have an out. He was low on life, but if he was able to block any of my creatures, he’d be able to bounce back through lifelink. However, he was also tapped out. So, I made an alpha strike and killed the creature he blocked, so that he didn’t get to deal damage and thus gain life.
I had two [scryfall]Lifebane Zombie[/scryfall]s out against an Esper deck. This is always risky, but I did it because I knew he had two copies of our most hated enemy, the aforementioned Baron, in his hand. Of course, he drew a [scryfall]Detention Sphere[/scryfall] and targeted one of them. Sphereing one meant the other was gone too, so I killed the one my opponent targeted.
This one I saw in coverage: Two Esper decks fighting each other. Each player had an [scryfall]Elspeth, Sun’s Champion[/scryfall] out and each had been able to amass a huge army of 1/1 soldiers. So, one player decided to kill them all with a [scryfall]Bile Blight[/scryfall], but instead of targeting an opponents soldier, he targeted his own, because he didn’t want to let his opponent use a [scryfall]Devour Flesh[/scryfall] to get rid of the targeted soldier. If the opponent targeted the player with the [scryfall]Devour Flesh[/scryfall], he could always choose another soldier then the targeted one to eat.
… and then there’s all the situations where you just need the few points of life and [scryfall]Devour Flesh[/scryfall] abides. This is especially good against Rw Burn, if you are playing cards like [scryfall]Desecration Demon[/scryfall] or [scryfall]Gray Merchant of Asphodel[/scryfall].
Also, there’s a new trick in the horizon. [scryfall]Silence the Believers[/scryfall] is a card from Journey Into Nyx. It exiles target creature and all Auras attached to it for four mana at instant speed. On top of that, it has strive, which is pretty much like a yet another multikicker, where you can target extra creatures for three mana. Therefore, perhaps you can (in the future) save your [scryfall]Nighthowler[/scryfall] or [scryfall]Herald of Torment[/scryfall] by killing the creature they are attached to your self.