Keeping the tank above 50 isn't keeping him "topped off" or "overhealing." In cases like Bene it doesn't disrupt your DPS at all; it's just a bit less potent if you use it early, but it'll also be off CD again a few seconds earlier in the run.

All you're accomplishing is making the Tank second guess your focus. I'll trust friends and people I run with a lot when they play pointless games with my Health bar, but when it comes to randos in the dungeon queues I'll just heal myself.