Because sometimes you're the one most effective against whatever's attacking you then and there, or people need healing immediately? I try to do it between battles, myself.

[Sniff sniff~ He'll take a bite before following up on that.]

If you're going to learn magic, it'll pay to learn about elemental affinities like that. Creatures can be weak or strong to different kinds of energies--sometimes they can even be healed by certain spells, or bounce them right back at you.