Basically yes - I cannot envision a user activity that doesn't create at least some CPU activity.
However this view might not contain all of the unused VMs. You might have a VM that is not used but have some scheduled job (example: antivirus) that creates some CPU activity and prevents the VM for entering the Idle VM list.
What I would recommend is:
1. For VMs in Powered Off list - most obvious candidates for deletion.
2. For VMs in the Idle VMs list - most obvious candidates for power off. Then in a month you can do another loop and delete again more VMs.
Thanks,
Alex D.