It's interesting to have information about your loyal clients, that's why Clerk registers all your customers consumption history.
When booking a new reservation you can see the two last stays of this clients. This will help you to remember and know in one second when was the last time he was in the hotel and how much he spend.
For more details on a specific client go to the "clients" tab on the main menu of your Clerk account. Search on the data base the profile of your client.
You will see some personal details and at the bottom the listing of all bookings registered by this client. Use the lens icon for entering the Checked-out reservation and find out what breakfast did he choose last time!