Ableton's official Learn Live series walks through every meter and indicator in Live's top-right performance panel, explaining exactly what each one tells you and how to act on it. The CPU Meter shows only audio processing load, not the full system picture, so if you need to see total resource usage you'll want Activity Monitor on Mac or Task Manager on Windows.
When Live's processing demands exceed your system's capacity, the Overload Indicator lights up with 'CPU' and you'll start hearing crackles, pops, or silences, collectively called audio dropouts. You can toggle between an average and a current CPU readout from the meter's dropdown, and the current view will always look more active since it reflects moment-to-moment spikes.
To find which tracks are hitting hardest, click the small C button at the bottom-right of the Session View mixer to reveal per-track Performance Impact Meters. This is the fastest way to isolate problem areas without guessing.
The same Overload Indicator also flags disk issues with a 'disk*' label. Mechanical drives and slower external connections are the most common culprits, so storing your sounds on an internal SSD is the practical fix. Keep at least 10% of your drive's capacity free as a baseline, with more being better.