IF you mean running something like a swamp cooler, watch out!
During veg, in an area that is already quite hot and dry (less than 20%RH), it can be beneficial. You will have to exhaust all that humididty out of your room RIGHT at lights out though to prevent dewfall and potentially fungus. Pythium, verticulum, and fusarium wilts are VERY common in greenhouses.
In flower, add the danger of grey botyris mold (bud rot) and it becomes too risky to run a mister system.

So to summarize, unless you can guarantee that you are keeping your relative humidity below 65-70% at all times in veg, and below 50% in flower, especially at night, don't run misters.