Depending on shape it adds 5-10 years to your apparent age
Beard adds 5-10 years to your apparent age. Every time I let mine "out of control" I get the SWMBO grumbling that I look like a pensioner (not that I care).
There is one more reason to have it.
Beard is useful if your jaw was not reset properly by an orhtodontist intervention at an early age (for whatever reason). In this days, glue-on-braces make orhto nearly always successful. That was not the case in 30 + years ago when you had to wear those horrible plastic mold things with stretch/pull screws in them. Any normal kid would just refuse to put them on after a few months of torture.