It would be nice to allow nesting of groups. This means that groups can be part of other groups.

Example:

Group A contains group1 and group2
group1 contains host1 and host2
gropu2 contains host3 and host4

In the overview you can choose between these groups, meaning the 4 hosts or just 2 of them.

This can be useful if you have a lot of hosts and want to order them a bit.