One of my special pet peeves is BLMs and SMNs stopping to cast weak Physicks when they ought to be DPSing.

If the healer(s) clearly can't be bothered or trusted to save you and that tiny heal will make the difference for the next hit, sure, go for it. But most of the time I watch them die to avoidable damage while standing there trying to self-heal from otherwise non-lethal damage.