Suppose you have a pedestal pump bolted to a cover plate.
The plate edge is 2' from the pump bolts. 8 of them in a circle.
You gotta lay down and reach the nut over from underneath, while you reach the bolt with the ratchet from the top.
Its called millwright crucifixion.
I used to use duct tape, and tape a nut to a wrench. Not so tight you couldn't get it off, but tight enough so you didn't drop the nut into whatever goopy grunge you were pumping.
Guitar amplifiers are pretty old school and often have long bolts though the chassis and outer case, with loose nuts on the other side. So you have to do a mini version of the crucifixion move. That is what these are for.
Other audio gear does too. I suspect large scale video gear might be the same thing, but I never worked with that.
yours Scott