I've only left groups twice, the first was a Stone Vigil run where the tank was somehow unable to communicate and would only ever tank one mob per pack (and fail at even keeping that single one under control a lot of the time). The second was a Dusk Vigil run with a tank who wanted to pull way too much and I calmly explained that Astrologians have no throughput cooldowns and he'd have to consider his pulls a bit, to which he responded that I should just play another healer then. I left because I really couldn't be bothered with someone with such a shitty attitude, pretty sure he pulled a new pack and probably died just as I left too. I feel bad for the dps but he really had it coming himself.