Yes, instant cast spells, including those when not used in a combo are meant to be used on the move.
They are meant to slow/stop the mob from pursuing you.
Yoshi-P commented on how he wanted spell casting and mages to work in general, though I don't feel like looking for it.
He basically said what I outlined though.

Edit: Here it is (was on the same page we are posting on)
http://forum.square-enix.com/ffxiv/t...l=1#post506046