The BeatSync feature allows for the synchronization of the playback with the timing of the beats.
The beat timing is calculated via the playback information of the Cue.
For instance, BeatSync can be used to:

Switch from one song to another at specific times during playback
Change the volume on a particular beat

To use BeatSync, the following steps are required:
Assign the "BeatSync Track" and "BeatSync" to the Cue (sync source)
Create the process you want to synchronize as an Action

Currently, it is necessary for the BeatSync source and the target destination to be played on the same player.
Therefore, in order to preview this feature, enable the "Single Player Preview" or use the session window.

[Ref] Synchronizing Effects with the Beat

Selecting the BeatSync source

In order to use this feature, a Cue from which the beats will be used for synchronization must be played back. This is the BeatSync source.
If this source Cue is not found, the Action on the BeatSync destination will be executed immediately.
If there are multiple BeatSync sources, the Cue with the longest playback time that meets the criteria will be selected.

Calculating the beat

Beats are calculated based on the number of playback samples in the waveform regions.
Therefore, if a Cue with BeatSync has regions that are blank or with interruptions, the timing calculations cannot be accurately performed.
Be sure to use a Cue with one region per track as the BeatSync source.