For arguments sake, that Rune Tap that is 0% overheal probably resulted in 90% overheal for the healer that was casting on you. The proper way to RT is to watch your incoming heals well, then pop it if a bunch of heals land and you dip immediately after. Its about threat assessment. Just because your low on HP doesnt mean the heals not coming. If the heals JUST landed and you get punked and end up at half health immediately, then pop it... its way more effective that way. Don't overuse it to boost your self-healing though, if you do that it'll be on cooldown when you really need it.
Thank you for the patronizing and entirely unnecessary lecture. What makes you think that isn't what I was talking about?
And, for the record, if you're low enough on health to die to the next hit but high enough that a Rune Tap will take you out of the immediate threat range (a larger range than it sounds in most cases), it's far better to eat a little overheal from the healer than it is to risk death from a just-slightly-too-slow (or too weak) heal. The healers would agree.