I think the only use i would want out of traps is a field effect, slow down, do a field-based attack or reduce hit-chances for enemy spells (like 50% just phase out instead of damaging you) etc.... basically, traps could become magical weapons that we place, that take about 3 seconds to charge then deploy a field with a PLOP and OOMPH and that field stays there (use not possible on battlefields)
Basically, something to slow down or catch enemies in would be practical, also IF at all, traps should cost mana and not be a consumable