I have just carefully gone through the entire site selecting and deselecting the 'Include in user picker filter:' options in the Summary/Advanced Options of each group. I had supposed that this would cause deselected groups to not appear in the list of groups from which members could be selected when adding someone to a group or rota - or when using Advanced Options in the Address Book. But it apparently makes no difference whatsoever to these settings, irrespective of whether or not I check the 'Hide group selection on user picker' check box in Settings/Users/User Picker.

I've searched this site for any reference to 'user picker' and drawn a complete blank. There isn't even a help button alongside the item in the Group's Summary/Advanced Options section. So what is this feature, and what is it supposed to do?