With this option you can select the groups you would like to be shown in your timetable and calendar. Thus, if you have shared groups from other teachers, you can decide whether you want them to be shown or not.
You only have to access Settings, in the Calendars section, and click on the Groups shown in Timetable and Calendar option. In the modal window that will pop up with the list of all the groups, you will have to unselect those groups you want to hide, because all are shown by default. Shared groups are identified so you can know which are which and can decide accordingly. The groups you have chosen to hide won’t be shown neither in the timetable, the monthly and weekly calendar, nor in the general planning option.