One very powerful feature in EM12c I think is Administration Groups. It allows you to do a setup of monitoring settings that is continuously up to date.
Monitoring Templates as part of a Template Collections are instantly applied as soon as a Target become member of a Administration Group within its hierarchy.
One issue you could have with the setup of an Application Group Hierarchy is that, after creating it you could not change it anymore and had to delete it before being able to make corrections or extend.
Starting EM12c 18.104.22.168 we can now modify an Administration Group Hierarchy after is has been created, which I think is a very welcome enhancement!
In the example one level (Location) is added to an existing Hierarchy. The message in the page indicates that the change need to be save to the repository by pressing [Update]
After pressing the [Update] button a message shows up, telling you a job has been started to reorganise the Administration Group Hierarchy and you need to wait for it to finish.
After the job has finished and you redisplay the page, the modification is completed.