1) No reason not to. I honestly lol'd @waste of mana since it comes back in no time at all, can go oom from holy spamming slowpokes/afkers to full mp in a few secs.
2) In very rare circumstances where a medica will do the job, the gcd saved > extra mp spent due to movement and/or incoming heavy damage to tank or party. This is almost as silly as the the first. As long they aren't going oom or causing the bard/mch to ballad/?, why care? It's not like they're casting medica when obviously a cure III was needed, or cure III on a single target.
3) Left for dead once because they were a liability. Otherwise it's because swiftcast is on cd. If the main tank is a PLD/DRK and awesome, that they hollow/dead I'll hardcast raise
