Just like the way softener sheets leave a residue on your clothes, they also leave residue in your dryer. However, it will not permanently damage it but may reduce its operating efficiency. If you do not clean it regularly, then the damage may become a reason behind the prolonged issue. The residue left by sheets may clog the screen of the lint filter. It may reduce air circulation as well. Hence, you should clean it at least once a month so that you can keep your dryer in a fit condition always.