It is not difficult to use abilities within miliseconds of when they come off cooldown; you just mash that button real fast when it's about to.
The only good reason for why you wouldn't use it the second it's up, as in planned for use right after a cast-time spell, or just whenever if you're standing there without anything useful to heal at that moment, is if you really can't justify its use at the time because you're in the middle of an epicenter or a breath of light or something. But if it's the case that, even when you spend up to 1/3rd of the fight in situations like that, it's still just as strong as mindbender, it looks like no contest to me.