Quote Originally Posted by dragonflyseksparade View Post
Why would you do this? If you use thundercloud first you could potentially get another thundercloud immediately. Whereas you will not get another Firestarter proc until you go back to Fire I spam.
Thundercloud's effective potency is 17 potency per tick. Every tick of Thunder (and you are not already under its effect), you are adding 17 potency to your rotation.*

Scenario 1: Thunder has three ticks remaining and Thundercloud is used, refreshing duration for 6 ticks.
Total Thunder duration: 6 ticks.
Total Thunder duration with Thundercloud proc down: 6 ticks.

Scenario 2: Thunder has three ticks remaining and Thundercloud is saved until Thunder expires.
Total Thunder duration: 9 ticks.
Total Thunder duration with Thundercloud proc down: 6 ticks.

Immediately casting Thundercloud decreases the effectiveness of the initial Thunder cast. The only reason I can see for immediately using up this proc is if your rotation would be interrupted negatively by saving it until Thunder expires.

*5% of 340 is 17. There's a 5% chance that every tick is a bonus 340 potency and full 18s duration Thunder.