Can anyone explain the inherient advantages and disadvantages of both systems in a VX?

I'm not real clear on what a supercharger does, so perhaps someone can start there... and explain why one system would be preferred over the other (or both?)

Plunking down $3k for a S/C is a fairly big decision, and not one I'm sure I want to go with. Installing and tuning a NOS system would probably be about the same, so it's a toss up.