Possibility to mark a usergroup for "not selectable"
I know that if You are select all, the groups are selected anyway - but this option is for a system where no one, but the users belonging to a group that is selectable will/should create events.
It could be so that the system warned when creating an event with a user that will not be selectable.
Could be used to schools, where You want each teacher to be a usergroup ( so they can be seen in public view )and don't want to see :
admin
Manager
no access
Post all
Post own
Read access