I think there are 2 advantages
1) a wbfs partition does not support fragmentation of games, so if u remove games, if you dont add a game of the exact same size right away you will be wasting space on your hard drive (but since oggzee says there are no advantages to fat, i wonder if this has been fixed)
2) fat32 can be managed via windows explorer, it can be defragmented, and once the games are in .wbfs format, you can transfer them to other external drives without the use of a wbfs manager
and 1 can think of 1 disadvantage
1)If you create a game specific channel (using Wiicrazy's "CRAP") that loads from fat32, you will get a configurable loader splash screen before the game loads (which only lasts about 3-4 seconds). Whereas the channels that launch games off of a wbfs partition do not have a splash screen, they just launch the game right away.
in the end, these are all minor advantages or disadvantages