A rush tactic, for the scouts to rush in and cause chaos to that nest.

Maybe, that the smoke makes sentries undetect anyone while it's surrounded, and the smoke is only smoke. The cool down can be a 45 second cooldown to 175 second cooldown, making this being used cautiously.

Hell, maybe those LED sentries on the workshop can see through the smoke but deal half or a third less damage when NOT in smoke, and normal damage when IN smoke.