I decided recently to give learning some of Jimi Hendrix's Villanova Junction.

Looking around the web everyone seems to imply that he tuned down half a step.
If this is the case can someone explain to me why ?

I really don't se the advantage in this.
it could be any number of reasons. like it could have suited his voice better. or it could have been because it was easier to bend the strings during the solo.

could be anything really but these are the most likely reasons.