It's pretty striaght forward in its usage, use it to to the raid off after a big hit where there is a lot of downtime and everyone is stacked.

Bismarck: after his limit break/getting chucked off his back
Ravana: chandrahas or the move after pillar of heaven(the one you stack for)
A1s; first phase when people can stack
Etc

You can use it for free heals during fights but assuming there's outgoing damage its a red flag for your healing partner that he's on his own(I often poke fun at my AST partner ror doing it in a2s).