Quote Originally Posted by Ultimatecalibur View Post
It is to reduce button bloat. 10 abilities that can be swapped in and out of 5 slots only take up 5 buttons.
Based on what we've seen of the interface, this doesn't look to be the case, unless users want to change up their hotkeys. Speaking personally, if I used 10 abilities but only five at any one time, I'd assign all 10 hotbar spots - because I would memorize where Esuna is, say, and I wouldn't want it moving around based on my spec on any given day.