Giving characters a distinguishing feature or mannerism increases your story’s imagery and provides a handy mechanism to remind readers what they look like. This can be something like their hair color or style; other distinguishing physical features such as eyes or nose; or certain gestures.
The more characters your story has, the more important it is to give them each some sort of “tag” so readers can keep them straight. With the possible exception of red herrings in mysteries, everyone in a story needs to serve a purpose and move the plot along. If they don’t, zap ’em, and if they do, make them memorable.