Prologues never did Chaucer any harm, generally speaking, but all in all I'm against them.
For some reason they work better in films or TV than in a book. They can set up a scene, or deliver some nice misdirection, or alternatively scatter some useful clues. They can establish an atmosphere. A picture is worth a thousand words and all that. A friend who went to see The Prestige, having earlier read the novel, was amused to see that the opening credits – a panning shot of dozens of identical-looking top hats – essentially gives the entire plot away, but no one who hasn't read the book is going to realise it. Thus, later on, the switched-on viewer gets the "aa-aa-h!" moment of understanding. But imagine if the book started with a description of the hats – that would just be pointless. Eventually the reader would get it, but so what? And that's why the book doesn’t do that.
This is not to say I won't use a prologue, ever. I already have. His Majesty's Starship kicks off with a press release. It seemed the quickest way of setting the scene. So I'll allow a prologue like that – something that seems off-whack with the story in general, so that the reader is intrigued to see how the two tie in.
But prologues that are essentially missing chapters from the body of the book – no. The information contained within such a prologue should emerge naturally within the story anyway. Case in point – an enjoyably flawed work I've just finished called The Last Templar by Michael Jecks. This, I'm guessing, was meant to kick off a medieval murder series in the vein of Cadfael. And it does – I gather there are other books with the same heroes – but not half as well. Part of that is way the author populates fourteenth century Devon with time travellers who invite visitors in for "a glass of beer" and can pin their movements down to "ten o’clock" or "half past seven". (He does however know his technical details, like how houses were made and lived in at that time, and boy does he make sure you know it too. But there are exciting action scenes, and a couple of good bits of misdirection, and the way he describes the glooming, looming Devon moors makes them almost come alive as characters in the best Gothic tradition. Credit where credit's due.)
BUT: it's a three-murder mystery and the most significant of these was an abbot who was tied to a tree and burnt alive. The abbot's abduction by two individuals was witnessed and it soon becomes very clear to the reader that there are only a couple of people in the novel who could possibly fit the description. One of them is quite obviously a nameless gent we met in the prologue. Now, without the prologue, we might think "that looks like X … but he’s obviously one of the good guys and I can't think why he would do something like that, so it can't be." Meanwhile X's history could be revealed bit by bit and the reader would be caught up in the excitement of discovery.
But no. Thanks to the prologue we can immediately guess 95% of what happened with perfect accuracy, and see why X would do that, and so the rest of the novel – approximately half, or more – is a frustrating exercise of watching the hero be immensely thick until even he can't avoid working it out.
Prologues. Avoid, if possible.