I usually wear my GoPro attached to my Sweet Strutter helmet. The curvature of the helmet doesn’t quite match the profile of the curved GoPro mount. So although the mount is secure there is a pretty good chance that a hit will knock it clean off. I have therefore installed a leash system.
There are a number of arguments for and against attaching the camera with a leash. Most of the against centre around the risk of snagging. At the end of the day I have thought carefully about the pros and cons and have decided that I will use a leash.