You're not supposed to be sure what a 'thing' is. When one wishes to be all inclusive, one will use a general term.
We're talking disconnects. In a broader sense, this discussion can apply to other devices used to shut off power ... such as valves. Safety interlocks. Blocks & clamps (for spring loads). Etc.
The issue does not limit itself to motors. Or compressors. Or heater elements. Or radio transmitters. Or ... well, you get the point.
Whatever needs stopping, I want the means for stopping it to be where I am at the time ... not three floors up, down the hall, in the third room to the left. The effect of this is to make multiple disconnects a sensible idea.
Besides the natural temptation to do as little as possible, there is the inevitable presence of Mr. Murphy on every job site. The more complex the application, the more chances there are for Murphy to make his mischief.
