My use case:
I want to track the CPU usage of serveral processes which use more e.g. 5% CPU.
Therefore I plotted the CPU usage of these processes in a stacked graph.
The stacked graph tells me about the CPU usage of the tracked processes, but all other processes are not monitored.
Thus I want add an item which sums all other processes. This is possible by creating a calculated item which subtracts the CPU usage of all tracked processes from the total cpu usage.
However if a new process is added to the tracked processes, one might easily forget to add the subtraction to the calculated item.

I suggest to add a feature which allows to sum up all items in application.
If this would be possible I could assign an application to all the tracked CPU proccess items and subtract the sum from the total CPU usage.
In this case the CPU usage of an additional process could be easily added be simply cloning one CPU usage item of an already tracked process. The application would be adopted by the cloned item and the graph would be adjusted automatically.

This feature would be much like grpsum, but for applications.