Well it never helps
Seriously though, a light amount of smoke won't have much if any effect. Think about speakers and subs and amps that are up on stage for any rock concert or big stage performance. Those things get bathed in fog machines, pyrotechnics going off, all the smoke in clubs and stuff. And they keep on functioning just fine!
But if the smoke is thick and dirty enough to leave a film or coating on any external surfaces that you can see, then you've got to realize that it will have also coated any internals of your speakers that the smoke was able to reach with the same stuff! That could potentially lead to some issues with the leads of wires, the strength of some of the magnets, or just the movement of the mechanical bits of the speaker. It'd be a good idea to clean the internals of any smoke-bathed speakers as quickly as possible after the smoke-filled event. Just some compressed air to blast out any of that particulate in the smoke that might otherwise settle and potentially corrode exposed metal parts, or cause increased friction or squeaking in any of the parts that can move.
Any airtight, sealed speakers should be unaffected. You could just wipe down the external surfaces of any sealed speakers or subs to remove any residue.
It's like anything though, just keep 'em clean. Don't abuse them or leave them all dirty or allow them to corrode or get all gunked up
Smoke won't do much damage. But getting rid of any residue as quickly a possible before it had a chance to settle and get caked on is a good idea
