Is a a brand new home or a new to YOU home? It might have powered a
shed, pole light or something at one time if your home is used, which
is mnore likely since you talk of newer breakers. in a brand new home
all breakers should look the same. besides no outside outlets is a dead
give away its not brand new all new new homes have outside outlets
see i am a excellent detective.
if it doesnt effect anything then leave it off permanetly or ideally if
you know how disconnect the black hot wire from this breaker so its
never powered on again by accident, like something triips so you or
someone else reset all the breakers that are off.
a friend had that happen at their home, AC tripped off after a power
surge, a family member reset all the tripped breakers, one of which
happened to be a long abandoned sauna, the home burned down:(
So if you can do it or have it done disconnect that line for future