The Scheduler shows you in calendar format an overview of meetings/events and function room availability. However, when you have a lot of meeting rooms, you have to keep scrolling through a long list, which is not only cumbersome but also is a waste of time.
Parent Resource Grouping allows you to group your meeting rooms together. It also allows you collapse and expand the 'parent' meeting rooms; by collapsing, you can see if any of the 'family' meeting rooms are blocked together by the same client, and by expanding, you can see the details. You also no longer have to scroll down the page to see the availability of all of your meeting rooms.