pfSense

Interface groups are only usefull now to add firewall rules to multiple interfaces. Problem is that when you want to add a rule, you often pick the source or destination address/subnet from the dropdown-list stating "_interface_ subnet" or "_interface_ address". It is not possible to select "_interfacegroup_ subnet" or "_interfacegroup_ address"

As far as I can see in the PF documentation, it is possible to use interface groups this way. I think a small modification of the pfSense code should enable possibility of creating such rules.

Same thing for Floating rules btw, one can select a number of interfaces to let the rule apply to but it is not possible to use the addresses / subnets of the interfaces in the rule.