This mode gives you two features in one:

  1. You can use it reset the downbeat of the Ableton Link timeline
  2. You can tap a tempo to adjust both the downbeat and the tempo of the Ableton Link timeline

If you just tap once, it will adjust the downbeat. If you then keep tapping, it will start to pick up the tempo and adjust the tempo of the timeline, too.

You could use this feature to tap along to a song you're listening to and it will bring the Ableton Link timeline into line with the song. You could then play along to the song using other Link-enabled instruments.