I'm a whm who usually tries to keep stoneskin up on all party members through a run. Its not hard and it doesn't delay the party any if you cast on the tank as the last mob dies.

For any dps who get hit i just replace as and when needed during battle, usually towards the end.

I never expect a group to wait for it. Even protect - if someone runs off and misses initial cast, I will just cast it later mid battle. Its really not a big deal and you don't need to wait for these things between pulls.

Having it on is nice. It gives me more time at the start of a pull to not need to heal immediately so I can Holy spam and stun mobs into oblivion.