IMO Dissipation is a DPS ability first. A way to sacrifice some healing to gain an extra 3 Energy Drains.
Secondly you can actually use it if your are out of MP, because if that happens it's most likely at the end of the fight.
And lastly you could use it to get a stronger Adloquium effect on your tanks and party. Though I would have to see a use for that yet. (In T13 it might have been useful)