Lightspeed is a great skill to heal while moving or even for burst aoe heal that drain a lot of mana.
I like using it as a second smili-swiftcast.
Sometimes, I even use it to spam some gravity, even if I know it reduce damages, it still allow me to do damages with less mp cost and while moving (and be able to instant cast a heal when i remove cleric).

It's also good to hardcast a raise since it has 5s cast time.