A lot of people I know say to put beacons on tanks and heal others... but i've found that not to be the most optimal way to play.. here is why...
The logic in the games code for the mana reduction (by healing a beacon target) (also the 4pce effect) happens as soon as you finish the cast. It is important to note that this fires BEFORE the number hits the player.
The logic in the code for the beacon heal happens AFTER the number hits the player.
Using the Glyph of beacon of course takes it off the GCD so you can cast a beacon in-between heals without losing a GCD.
so you can essentially trick the system into giving you both your Mana reduction/4pc stack and your beacon heal by switching beacons before the heal hits..
since this is the case why would anyone want to let a beacon sit on the tanks when you can micro manage them and not let them go to over healing, and get a little mana back while doing it... this does not require you to heal the beacon target either, you can heal anyone and micro manage by switching the beacon from a full target to a half target.. and if a tank happens to take a hit after losing the beacon well that just means he's my next holy light target.
my question is how publicly known is this mechanic? I can't assume that i'm the only one who has figured this out as I've been doing it since MOP to get free holy powers, as it worked then too.