I have always used a 4" vane with my 5575 Gold Tip Hunter arrows shooting a 100gr. Spitfire broadhead. I have been happy with arrow flight with this setup, but have noticed alot of people shooting 2 and 3 inch vanes with similar arrows and broadheads. Can someone tell me the advantage or reason why I might want to shoot a smaller vane?

If you're satisfied with what you have then you don't really want to know. It's nothing that magical.

It is all personal preferance. The short vanes like blazers give more stability to the arrow at longer ranges, and help to resist the broadhead from planing when using fixed blades. Since you are using the mech. and having good flight already, then there is really no reason to switch if your happy. If it ain't broke don't fix it!