Another downside to it is EMI. tying all the wires tight together increases the odds of any EMI problems vs letting them be loose in the wire duct.
In a previous CNC machine, I zip tied everything together very carefully, but was getting phantom steps in one of my steppers (even with shielded wires). Unclipping the zip ties caused the problem to go away. (after that, I added plenty of ferrites, too, as a measure of safety, but clipping the zip ties killed the only real symptom)
I had actually used EMI shielded wires - but, I think I must have had a faulty connection from shield to ground. Practically speaking, EMI shielding is hard to get right if you're not a pro. I only recently got an Oscilloscope and was able to measure what the EMI noise actually looks like on a wire. That helped a lot in getting rid of it, too. VFDs are pretty awful - the one in my machine nominally outputs 8amp,220v, 500hz power, containing that is a matter of extreme care. My previous CNC (now sold) really just didn't make any attempt and just counted on physical separation of wires and software filtering of signals.
Had a similar problem on a stepper motor motion control system in a vacuum chamber. The single electrical feedthrough forced motor and signal cables to be in close proximity. The pwm noise from the motors would couple to the opto isolated limit switch signal and force the limit switches on. I solved it by putting 10k pull down resistors with a bypass capacitor to ground on all the inputs. Phantom stuck limits were no more.
I’ve found recently that ferrites really help with this. The electrical noise from large steppers is really erratic, but responds well to ferrite beads with 2-3 wraps. I put one at each end of the cable, since back-EMF is very real in large steppers.
Regardless of wire gauge, bundles of wire noticably reduce your heat dissipation ability and therefore reduce your safe current carrying capacity accordingly. That's why electrical code significantly de-rates the current capacity of circuits which run more than just a few conductors in a single conduit or through the same hole.
In a previous CNC machine, I zip tied everything together very carefully, but was getting phantom steps in one of my steppers (even with shielded wires). Unclipping the zip ties caused the problem to go away. (after that, I added plenty of ferrites, too, as a measure of safety, but clipping the zip ties killed the only real symptom)