Personally I have yet to fill a single hotbar (for any character, including my mages) so I don't see the need. Will see if I do once I progress *much* further through the game.
I've done a caster/tank Lone Wolf pairing, so my caster uses all 5 schools of magic. At level 7 she has 22 spells. Definitely a hotbar wrangler.
Meanwhile the tank has just 7 things on the hotbar.
