Number of visits allows you to be more specific on when, what, how, and with who the visit was vs milestone visits.
You can specify the status of the visit; late cancel, no show, check-in, absent, etc.
These behaviors can also be tracked over a time frame, and you can filter on the instructor, credit used, membership used, and class time.
Use case:
Creating an automation to upsell someone once they sign in three times using a class pass within the last month.
Creating an automation based on clients who no show their first ever visit.