A Command control has no state. It simply allows you to initiate an action. Unlike a Toggle, you cannot undo a Command. The most common usage of Command controls is to assert a preset.
You are designing an audio system for a church and have configured several presets containing different audio configurations for the sanctuary (Sunday Service - 9am; Sunday Service - 7 pm; Bingo Night). You want to give church personnel the ability to assert the appropriate preset depending on the current audio needs of the room. A list of Command controls works well in this situation.
note: A Selector Preset Group would also work quite well for this example, but we'll use Command Controls for now to illustrate how they work.
A DR2 works nicely for this scenario. The end user highlights the preset on the DR2 LCD screen and then pushes the DR2 knob, which asserts the selected preset.