IMHO not unless you're really having problems with it....before a fresh load. Otherwise, just leave it be. Remember the adage "if it ain't broke, don't fix it". It applies here.
It's an extraordinay amout of wear and tear on you drives mechanics to carry out the entire process of formatting and reinstalling everything for no reason.
You don't even want to defrag more than once every month or so
I think it depends on the file format you are using. I have a XP with FAT 32 and find it could use defrag. every two weeks or so. But my PC with NFTS needs it even less often the once a month.