Don't answer terrible hand holding posts, report them instead.
The problem with reactive healing as a paladin is that we are primarily tank healers (and secondarily nothing we suck at anything else).
Reacting to damage a tank takes, means at minimum if you are more than human, your heal comes 1.2 sec after the tank takes damage. This is a real problem when your tank is taking more than half his life in a single shot, therefor it is more beneficial to preemptively cast your heal (and spam it) to land, hopefully, as he is taking damage, or at least in-between large boss hits. If we bring human reaction time and server lag, your heal can come a full 1.6-2 sec after he takes damage if you heal reactively.