A 4th team member is always a help.
Especially when he has unlimited hi-potions.

Vaan... yes his personality isn't the greatest, but maybe its just me or the other characters, it just doesn't seem that horrible. Then again, I've already been exposed to Tidus from X..... and it's hard to see fault in anyone else after watching Tidus for the first half of X..........

At least in my opinion.