If the loom is in excellent condition, things like this come in handy when u are doing an entire playfield strip etc.
You could use the loom to set up the new playfield and use the old one still attached to work out exactly where everything goes on the new playfield.
Also, if u have a machine in storage and the rats chew anything, this could be handy.
I know that guys who do pinball repairs for a living, like to get hold of full looms for various manufacturers cause they make up test benchs using them. I have seen Beaky(Andy) build various test benchs and it has been very successful.
As Marty pointed out, often good to have the spare loom when fixing hacks done by overseas bodgy techs.