Brushed motors wear their brushes down - however in some cases it may help prolonging service life by performing a “break-in” to have the brushes form to the commutator fully.
Generally speaking:
Run it gentle (low rpm) and without much load for the first few times, this allow the brushes to wear down uniformly (relative to the commutator). High power load early in this process can cause uneven wear/increased spark within tool. This reduce efficiency and increase in brush/commutator wear.
YMMV 