Sometimes customers can run out of credits before they're subscription re-ups at the end of its renewal period.
If you've created a limited use auto-renewing subscription (ex. 5 classes a month), you may want to allow over-booking. It gives that customer that's run out of credits the option to keep booking classes and "put it on their tab".
For example, if a customer was on a limited-use subscription that gave them 5 classes a month, and allowed for over-booking,
they could use up all their credits before the end of the month
and could then book, say, two more classes using the 'overbooking' option
This would result in the customer paying the normal subscription monthly charge plus the cost of the drop-in fees for both of those additional classes, all billed at once at month end.
If this is something you'd like to offer your customers, edit a subscription and make sure it has:
the usage limit toggle on
the number of classes or appointments set
the 'auto-renewal' setting on
Then scroll down to toggle on 'Allow over booking' > save changes.