In simpleERB for staff user logins, you can set 3 different authority access levels; owner, manager and waiter.
Owner users have access to the full system for booking/setting functionality and there is no restriction.
Manager users have access to reports, settings and the ability to 'manager override' certain functions/changes such as but not limited to; overriding max covers on a table, table joins that are not set in place, make changes to locked bookings and make a booking in a time slot that has a compromised stay time.
Managers do not have access to the accounts billing plan/usage details, staff username settings or the ability to upgrade account plans.
Waiter users are only able to make and amend customer bookings. They don't have access to settings and are unable to make any booking changes that conflict with the settings you have in place. Therefore they can't add bookings once the cover allocation has been reached for a time slot and they are unable to override booking covers on a table.
If you wanted to add another level of authority to simpleERB, please see our article here about adding PINS or restricting booking cancellations.