Don knows his stuff! I've used midi in a variety of band situations. I've used it as a simple scene selector using a foot pedal to select bank/program steps. It's OK but you have to really think out your bank setups. I ended up with about 6 or 7 standard programs (e.g. slow chase, fast chase, blue show, red show, etc). My current band is using a sequencer for drums and background parts. Now I'm moving to designing midi controlled shows for each song - because the sequencer can drive everything. To get more control with midi, you need to step up to something like the Show Designer. As Don said, the Operator can only do scene/chase selection. The Show Designer can do programed fades, do timed sequences, etc. It also has more scene memory than many other controllers.
The only real advantage to midi control of an Operator is a) if you are already using a sequencer or b) you need to have "hands free" scene/chase selection (using a midi foot controller or something).