i got a question for you dps..

[Aiselia]

an add spawns

you're better off using it for add spawns

Assuming a single boss encounter

'Round my parts, "single boss encounter" means that there's only a single boss for the encounter, no adds, so you wouldn't need to save it for adds in a single boss encounter, so, I mean, unless "single boss encounter" means something different for you, there's that context.

If I use it randomly just because the cooldown is up

I'll precast it for my opener but past that I won't use it unless I need to.

so the tank could keep aggro on initial pull

Initial pull isn't "using it randomly". Initial pull is where openers tend to happen.

Hooray for context.