Since some people think “it’s simple,” I’ll expound upon why I think it carries an opportunity cost that’s almost impossible to evaluate.
If you are, say, a Frost Mage, casting Frozen Orb or Blizzard is basically a question of whether there are enough enemies that will live long enough to justify the GCD/cooldown. That’s something a player could reasonably intuit or figure out. Abilities like Whirlwind or Blade Flurry are even simpler: when you see AoE, you press the button and do damage.
With Implosion, you are trading all of your imps’ single target damage in. The amount of damage that spending that GCD does depends on the number of imps, which can vary, even as you are going to press the button since they despawn whenever they finish their casts (this specifically is why the developers are changing the imp energy system in Midnight). It depends on the number of targets, like all AoE. It’s also quite possible for the AoE to not hit all of the targets in a pull, which is not easy to observe given its visual effects or lack thereof.
And you are weighing some notion of how much damage that singular ability use does versus:
- what damage those imps could have done if you had allowed them to stay alive, which is fairly significant, and
- spending those GCDs instead to push towards faster HoGs, which equates to more AoE cleave from, e.g., Diabolist summons.
Blizzard recognized one small part of this in the first sentence of their Dev Notes as quoted earlier. Unfortunately I don’t think their changes in Midnight address all of the core issues, while simultaneously attempting to steer players towards needing to use Implosion. It’s going to need some major revisions (or more realistically, a good alternative) for me to change my mind.
FWIW, it basically never mattered this expansion unless you were aiming for very high end content.
I was regularly at the top of the damage meters in the M+ runs I did while never using Implosion a single time. It’s not a special feat, especially on these forums, but I cleared 2500 M+ score last season in delve gear without making any sort of effort (I was just helping a friend who wanted the achievement).
Maybe my anecdote is not convincing enough for some folks, so I simmed it on Raidbots to double check my personal experience over the past year.
If you were to use Implosion vs. never using Implosion in sustained 5 minute fights:
5 targets: 4.4% increase in damage
3 targets: 1.4% increase in damage
These numbers are if you never missed an enemy outside the 8 yd. radius, do not factor the enemy count dwindling over time, and notably, assume you were pressing Implosion with algorithmic perfection that I am arguing is incredibly unrealistic for most players and most fights given the way the skill is designed.
If your group does massive pulls where seconds matter AND you are loaded up on addons AND you are attuned with the Loa of Implosion, then it might be important. Otherwise, the difference is fairly negligible.
(TL;DR) I stand by my statement that the ability is terrible, hard to use correctly, and add that it hasn’t mattered much overall.