For example, if you use the code "CHECKEDIN" when guests check in and "CHECKEDOUT" when guests check out, you could create a custom reports to show custom reports by showing booking which include the info code "CHECKEDIN" and excluding those that have the info code "CHECKEDOUT.
You can also use [[Template_Variables|template variables]].
Preset info codes can be defined in SETTINGS->ACCOUNT -> PREFERENCES "Booking Info Code Presets "