Toggle Hide Group 1 ⌃⇧1
Toggle between showing and hiding the channels and tracks in group 1. NB the hiding of tracks is further controlled by the Hide button. When the Hide button is disengaged (green) tracks will not be hidden. The Hide checkbox on the track will be enabled or disabled as appropriate.
Hiding channels in the mixer windows can definitely help keep things from being confusing.
You can hide and unhide tracks using the menu commands in the Track menu (Hide Track, Unhide All Tracks, and Show Hidden Tracks), or using key commands. The first time you hide a track, you use the key command, after which the Hide button appears above the track headers.