There's a kind of prologue that kicks things off with something active and immediate and maybe present tense, and it's all very exciting, and then the first chapter starts, very stodgily. The prologue feels like a lazy way of dealing with a problem, instead of re-writing the damn first chapter. Or if it's the kind of prologue that's after the event, ('Long afterwards, I realised that...'
it can be a lazy way of setting up narrative tension, by providing a hint of a juicy part of the story, so the reader then is titillated into reading on.
I think I would be tempted to examine this potential prologue very fiercely, to see what I was trying to do with it, and whether I couldn't do it more fluently as part of the body of the story. But I quite often find I want what you might call a nearly-prologue, with the narrative voice at first looking back at the story from much later before slipping into a more immediate-sounding straightforward narrative past tense.
On the other hand, they have their uses as a clean way of setting out a back-story, rather than that awful zig-zag back into the past that writers do three pages in: 'She had come down the stairs one Monday morning three years earlier...' Or yes, to have an alternative angle on the main story, though Dee's got something, in thinking that the reader may need reminding of that alternative take occasionally, and Terry's right that you need to know who's view it is.
Emma