It depends how capable the other group members are. Most of the m+ ive been in ive had to heal continuously as everyone takes heaps of damage.
Unfortunately If your group sucks, you have to heal non-stop to keep them alive and it may still not be enough.
But if your group communicates and coordinates stuns/interrupts well, you have short windows every pull to help them with some DPS. It's not much, as resto druid im usually somewhere in 60-150k bracket depending on how much I need to heal, but it may cut a few much needed seconds to get another chest. Staying idle while mobs are stunned and everyone's HP is topped is just lazy, and anyone doing so or saying it's ok to be pick their nose while others are trying to beat the timer, should stay the fuck away from M+ queues because they're potentially crippling any group they join.