Healer Role in Dungeons

[Teraluna]

Please can someone help me to understand the healer role in dungeons. I thought my job was to just heal my team members but I've been told twice now that I'm healing too much. However, if I don't keep on top of healing, the tank dies and then I get a load of abuse. I'm not sure when exactly I'm supposed to heal if not when it's needed and why I'm not supposed to keep everyone's health at 100%?
Any advice would be helpful, thanks.

You can heal....but - your major role is to take the blame, it is in the small print when you agreed to take on the healer role.