Show/Hide Track Stacks
Use this command in the Mixer window(s).
In my simple test project using the command simply hides the track stack indicator at the bottom of the channel strips. It does not hide and of the tracks included. I expected a different behavior.
I am not sure of the utility of this command, unless the vertical real estate in the mixer window is so highly regarded that it needs to be here.
Track Stacks provide a convenient way to organize and control tracks, to manage projects with high track counts, and to create and manage audio subgroups. You can create a Track Stack from a group of existing tracks, and use the controls on the master track to control all the subtracks in the Track Stack.