The Line 6 M13/M9 stompbox modelers are incredibly powerful and versatile units. But with up to four effects active at once, sometimes you want to turn more than one effect on or off simultaneously. Unless you have VERY fast feet, this can be difficult!
The solution is to use scenes. Store one scene with all the effects you want on simultaneously, then store another scene with either those effects turned off or other effects turned on. Now, when you switch between those two scenes, all the effects will switch at once, with one button press.