What is the difference between summoning an unbound dremora and conjuring a dremora lord besides the obvious reasons being ones two handed and one takes longer.

If I'm not mistaken, unbound dremora only works for the conjuration master quest on the roof, whereas dremora lord can be used everywhere and is actually useful.

If I'm wrong, someone please correct me, but I don't think I am <.<

so theres no use to the summon unbound dremora spell except for the quest?

yep, it only works on that roof too. you can't summon them elsewhere, not that they would serve you even if you could.

I wonder if you can summon an unbound Daedra that was off-duty? Or do they all stand around waiting to be called?

Like, instead of appearing in armor with weapon in hand, you summon one sitting in a lazy-boy, wearing a bathrobe and reading the Daily Daedric Times.