What is a Group?
A group is a way to refer to multiple channels, not in terms of a look or specific settings, just as a … well … a group.
You might create a group for an entire system of lights. “Grab all my front lights and take them to full”. Or it might refer to a subsystem. “Grab the backlights, but only the ones that are downstage”.
These are used to speed up the process of programming, to save keystrokes, to make your life easier.