Generally speaking, yes, however that depends on your installation and maintenance method. For free form dreadlocks it could be beneficial since it is compressing and tightening your dreadlocks. For the twisting method it is very bad because your twist will come undone. The crochet method is the least effected by wearing a helmet. If you wear a helmet with your dreads often you should also be aware that there is a possibility of forming flat dreadlocks.