If I take Primal Elementalist when should I use Empower?
Empower has two functions: give Restoration Shaman something to take Primal Elementalist for, and to give you a damage buff when your Fire Elemental can't hit anything. The only way you'll be able to use Empower all the time is if you can somehow do eight times your average DPS for the entire duration. eg: in T14H gear the Primal Fire Elemental deals about 40,000 dps. You'll need that to be 5% of your output (or 800,000 dps) for Empower to be useful all the time.