There are a few advantages. You can allow access to most non-customers but refuse heavily intoxicated people. The McDonalds near me sometimes has to call an am

There are a few advantages. You can allow access to most non-customers but refuse heavily intoxicated people. The McDonalds near me sometimes has to call an ambulance due to an overdose or medical distress in the bathroom. If there was no access control, it would be less likely to notice someone not leaving the bathroom in a timely fashion. A bathroom OD isn't great for business, but a dead body is worse.