My take, be vocal. Whatever is what you are going to do, communicate. Throw in a "Hey, guys, I'm going to use lb on next pull so it fills against for the boss and we save some time", wait for any answer and proceed with the most fitting action.
I'll tell you a "reverse" example. A pull on Arboretum's second Honeycomb, I was paired with a BRD that didn't AoE during the whole dungeon to top it off:
I started my rotation with full opener because seeing BRD's dmg, we couldn't do it without at least losing the tank. After I popped all my shit and went to 1/4-1/2 of its HP with the opener, the Tank starts saying "LB". I didn't do it because I popped everything except Battle Littany and would enter the boss without buffs at all. So goes BRD at less than half hp and unleashes his LB and I end up going into the boss without a single jump or cd.
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