This could be used very good for player Spells, i mean, spells who you can aktivate by click,
they can be used only 1 time, with researching, you can get new spells,
like:
fire explosion,
mana kill,
thunderbolt,
call stone golem (use only above stones),
earthquake,
Stone Rain,
Side changing (takes a unit of your opponent to your side till he dies...),
recover (recovers the health of all your units),
call magic thorn bush (calls a thorn bush, who can attack nearby units),
magic shield (gives an unit 100 extra life points, an building 500 extra health points)