Actually the misting due to evaporation is usefull .... obviously if evaporation has occured then the local atmosphere has been cooled ..... which is part of trying to tame the fire !!! ... if your working in conjunction with ground crews they are particulaly happy if you can occassionally COOL them down ...notwithstanding that water droplets in the vicinity also reduce smoke/particulates in the atmosphere ....they like that too!
There lots to this firefighting ...not all of it obvious!
Cheers