if you pull it right at the start of a fight it is good for just about any dps.

during a fight it's almost a total crapshoot if it will be good or not since you don't really have a HUD of everyone's cooldowns
but... theoretically it would have a pretty decent impact if you were able to land it just before one of the big mechanic based skills like reload, aetherflow, enochian, etc
again though, drawing the card and using it right in sync with one of them is total luck because if your waiting on it to use on them or they are waiting on their skill for you to spear, that lost time negates what spear would have gained.

it can be quite nice on your own luminiferous aether cooldown and it does lower draw's cooldown too.

In a practical sense, using it for the extended royal road is almost always your best bet