You mean the tab in the navigation bar? No, it is to filter groups that will have their members listed. Example: if you have a BANNED group and don’t want members from this group to show in the list, just don’t select BANNED there.
It reflects the total members selected in the setting GROUPS TO INCLUDE (above), as stated in the changes:
The FILTER doesn’t update this counter anywhere in the suite, AFAIK. Test yourself in Downloads (Marketplace on this site). Go any category and change the filter. It won’t update the counter.