I feel the rule is good as far as being able to find the disconnect.
If the rule is followed, at least you know the disconnect for something should be within a certain area.
However, when it comes to the safety aspect of working on piece of equipment, the disconnects physical location has little to do with safety.
The extra step of common sense and LOTO come into play at that point.
JAP>
And situation can be different in one place vs another. If I am in middle of a cornfield all by myself and throw the disconnect that is within 50 feet of me to work on the center pivot machine, the chance of someone turning it on are not that great, unless maybe a raccoon sneaks up and turns it on.
Being a 1 man show I am fine with that. If I had several employees, I may still want them to practice locking it off anyway.
I have also been situation on such application but needed to shut power off on disconnect at the road, which may be 1300 or even 2600 feet away. Might lock that one, might remove fuses from it so if it does get turned on still won't send voltage down to me, kind of depends on circumstances at the time.
Electrocutions I have heard about in above situations often was one worker at the road disconnect, one at the equipment and miscommunication on when to turn the switch on.