Sacrifices are good, as long as it isn't
*battle with slime*
Guy 1: HURRY, RUN! I'll distract him!
Guy 2: But we can both escape!
*slime attacks, guy one jumps in front of it to get hit*
Guy 1: AHHHG! No...No time...Save yourself!!
Ok exaggerated, but you know what I mean. If its the only way, and plausibly the only way, then the sacrifice works. Also, you need some depressing music, and it has to help some way. If the sacrificed person is a main char, especially one everyone likes, the sacrifice scene adds alot of emotional depth to the game, provided you've done the characterization skillfully, and properly pull of the scene. It's even cooler when someone we think is an antagonist sacrifices themself. Think Shadow form Sonic Adventure 2 Battle. An even better example is from a book called "The Wings of Merlin" (part of a series, the first of which is The Lost Years of Merlin). The supposed antagonist from the first book, whom Emrys (Merlin as a teenager) still hates sacrifices himself to save one of the main characters. It's a very well done scene, and adds emotion.
As you can see, I'm very opinionated on the subject, XD, I like sacrifices.