Think of “Group” commands for command and control. A given device or remote sends a command to another device or group of devices to turn on or off.
Think of a broadcast message as a means of advertising or monitoring. Some software packages use this scheme to know when something has happened in the system, such as an alarm from a water leak detector. No specific group or ID needs to be known and the devie simply sends the message out there for anyone intrested.
Most people will use group commands for control when not using a home automation package.