This device will observe if a clip is present or/not for a certain clip slot on the track it is placed. IF there is no clip present Ableton Live’s metronome will be activated. If you record a clip it will stay on. When you then re-trigger this clip the metronome will be de-activated automatically.
This becomes pretty handy when recording new loops e.g. via the One Button Live Looper. For most use cases you will need a metronome for recording your first loop. But if you have your first loop (or your second or third…) recorded you probably won’t need the metronome anymore.
Please check out the tutorial: