eh, the bar ends let you "pull" open you're chest more and allows you to get a little bit of extra air when you climb(note: this is what I was told by a fellow rider). They also help if you're bars are completely straight like mine are. BTW I would have gotten another pair of risers but these(my flat bars) were just laying around so I might as well use 'em.
The bar ends also let me get a little bit extra leverage when I stand up and climb. My flat bars are very narrow IMO, at 22" wide. My risers were 28".