Tridus basically covered it all, but I just wanted to add two points to Dissipation.

1) You can use it in your opener after you've burned through 6 AF stacks if the raid doesn't require much healing at the beginning. You need to consider the 30s penalty, and ideally you don't want it to force your co-healer to stop DPSing either. This is much more useful at lv70 though where you can use the Quickened Aetherflow trait.

2) Technically you should use Dissipation towards the end of every fight so you can gain 3 free stacks to push even more DPS. It's one of those no-brainers, but admittedly I forget to do this a lot of the time. :'D

Using Dissipation for its actual intended use is quite rare, and not really something you can plan. Though if you're using it only at the beginning and end, it should be up throughout a fight should you need to hit that emergency button.