Close unresponsive apps and processes
When your system is acting sluggish or simply not responding, an app or process may be the source of the problem. You can use Activity Monitor to locate the troublesome app or process and force it to quit.
See how much energy your Mac is using
You can find out how much energy your Mac is using, and see which apps or processes are using the most energy.
See real-time CPU, network or disk status in the Dock
It’s easy to keep an eye on your system status without even looking at the Activity Monitor window — you can monitor your CPU, network or disk usage as a live graph right in the Dock.
I often keep Activity Monitor running, with no window open but it sits in Dock with View > Dock Icon > Show CPU History setting. Then, if something is sluggish, with a quick glance I can see if something is taking a lot of CPU. And with another click the window opens with my preferred view – CPU column, and View > All Processes. A rogue process often takes too many CPU ticks and can be seen in the top of the table.