TP is the most cost effective heal in the game currently and should always be placed on the tank. If you know your tank has an agro problem or does not front load his threat, then you may want to pause before placing TP on him. I would not reccomend blowing your agro drop at the beginning of the fight. I prefer to save it for when adds are present or soon to be present
Yes, I am starting to realize that this no longer applies. I took a break for a few months and came back recently and just kept doing what I used to do. Previously, if TP was cast on the tank as he entered the fight you would immediately draw threat from everything else in the room, thus requiring a threat drop. That seems to have been changed, sorry for cluttering up the page with that nonsense.