Tony Vargas
Legend
Honestly, PrCs are primarily a tool for the DM - that's why they showed up in the DMG. A DM is fully within his rights to decline the use of any PrCs (if none of the published ones fit his world or style, for instance), indeed, I rather think that's the default. DMs may add published or original PrCs to thier world to give the world some unique color, and the PCs a chance to feel that they're more intimately a part of that world. The occassionally impressive powers of PrCs are there mainly as a carrot to encourage such, though, personally, I think it superfluous - a sufficiently cool PrC, that really fits the campaign world well should be quite attractive, even if it is only on a par with core classes.