It still will be usefull, think about a flat map, or reaching long distance on creative.
Autorun will allow your character just to go foward. You can be afk for 15 sec. or you can stay on your keyboard and still perform jumps or atacks. You need to feel whats it is to be on autorun, a simple task automatized.
You just can´t say that will be not used often, because going foward is the most used action on the game.