CPU and GPU readings show how much supported processing capacity is active at the current sample. They change quickly and should be evaluated alongside the task the Mac is performing.
Normal high activity
Updates, Spotlight indexing, media export, games, video calls, virtual machines, development builds, and photo analysis can use substantial processor resources. A short spike when opening an app is also normal.
Activity worth investigating
Look more closely when activity stays high while the Mac should be idle, the same workload suddenly takes much longer, battery drains quickly, or heat and fans remain elevated.
Use Activity Monitor to identify individual processes. Overview provides an aggregate signal and does not attribute every unit of work to a specific app.
Compare readings correctly
Observe the Mac under the same power mode and workload. Sampling intervals and multicore reporting can make percentages differ between monitoring tools.
Respond safely
Save work, close unnecessary tasks, allow known indexing or updates to finish, and update an app that repeatedly consumes excessive resources. Do not delete files merely because processor use is high.