Tanks that don't tank

[Grenwal]

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So should I share his target or pick off the stragglers (i.e. mobs that are healing his target)? Thanks for your patience
Edit: just found this and it explains my role and the on screen meters quite well: http://eorzeareborn.com/enmity/

[Urthdigger]

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Generally, you should share his target unless told otherwise. If you focus your DPS on a mob healing his target, you WILL wind up tanking that mob. Tanks take MASSIVELY less damage than DPS, especially at higher levels (assuming they are geared correctly), so you tanking a monster on the side means more work for the healer.

There is an exception though. Commonly in boss fights, there will be additional monsters (adds) that spawn. Typically, these monsters can be killed before they damage DPS too much, and/or the tank can't move the boss without endangering the party (many boss monsters have conal attacks that must be faced away from the party). As a DPS, you will almost always be needed to attack these additional monsters, even if it means tanking them.