Please may someone explain Working Time Plans in Quota

I've noticed that the setting for "Manage quota on the level of booking intervals" is only available with the usage of Plans in Quota and not when it is entered as a % of calendar for example

I have tried to find Working Time Plans in the system and have searched the documentation also but can't see them referenced anywhere. Please may someone explain to me briefly what they are and where to find them? Because I would like to set up booking intervals and use them to manage the quota but we were previously using the calendar for Quota