let's discuss ideas about guitar cable diy.

[PRR]

>> And the shield is only connected at one side to avoid ground loops.
> ...it's impossible to have a ground loop between a guitar and its amplifier because the guitar has no other path to earth ground except via the amp.

If the shield is doing hard work draining garbage, there is a voltage drop along it. Running a separate conductor for signal-return avoids getting the garbage added to the signal.

Yes, in easy situations it makes no difference and in horrendous situations it is not enough to notice. But there is a range where it helps.

Between two wall-powered boxes.... depends on detailed implementation of I/O jacks. In some very well-considered boxes a separate ground conductor makes a real difference. On the average stage-box probably no difference at all.