When guests have left you can check them out by clicking on the checkbox on the right side of a reservation
As you can see you can do 3 different things
Undo Check In
Select this if you have made a mistake checking in this guest and you want to undo this action.
Now you have a good view about who is still in your business and who has left.
Check Out and free capacity
You can take it one step further and automatically free the capacity so that the freed up seats can be booked (online) again during the same shift. This allows you to double book tables last minute.