The snapshot list:
This lists shows the available snapshots in the current session.
A “snapshot” is a complete recall all of the track, region, mixer strip, and plug-in information.
All of the snapshots share the same session audio data; this means you can have multiple “snapshots” ( i.e. songs, mixes, or remixes ) without recreating copies of all the audio data.
Single Click on a snapshot to switch to that snapshot.
Snapshots are also accessible in the New Session Dialog, when launching Mixbus. See “Starting a Session”