Good for warden if you heavy attack I guess. Otherwise, it is useless for templars because too slow.
I use it on my own healer for vet trials and vet dungeon runs. The light attacks heal over time, with the morph that heals you for any healing your allies get can help keep both of you up in some pretty crazy situations, and the heavy channel can for me do roughly 17k heals per second to keep tanks alive through anything but one-shots. It takes some getting used to but can be real strong.
I never grinded psjic enough to unlock it, but it doesn't look like it would be that useful. The main issue is that if you need to give them 5k hps, then the time to cast the spell, aim for them, and cast a heavy is pretty much only going to result in them dying. The light attack might be nice to add an extra hot, but rapid regeneration or mutagen is probably a better bet for just applying one of those. It might be good if you are like a DK trying to find a hot to add on top of mutagen. though, if you are a DK healer you probably have more concerns than just filling random slots.
If you are looking to add heavy/light into your rotation as a means of more effective healing you might like using a warden. Casting the lotus blossom will smart heal people as you light/heavy enemies. That way you do a little damage, regen magicka, & get major mending while you do the heavy healing. Since my warden healer is just one I fart around on, that's basically how I set it up with Vanus/guidence gear so a heavy gives me major mending for 9 seconds and the blossum makes sure it is healing a nice amount to the group too. Not a great build but fun to play.