Every time you strap two analog devices together an impedance interaction occurs that can alter the sound of the no-longer-isolated devices.
Imagine two devices that are fused together at the circuit board level. Without any cabling between them, their impedance interaction will still have an effect that renders the whole greater than the sum of its parts. When two analog devices become one, a new sonic signature emerges between them.
This is why changing the order of the analog chain often results in strong sonic changes, followed by even stronger opinions for / against one chain sequence over another.
What does adding a cable between devices do? Contrary to popular opinion, cable itself does not have a sound of its own. Cable materials and construction geometries give way to electromechanical properties that can exert influence over the aforementioned device interaction to the effect of changing the sound of the overall chain.
After many years of testing cabling between devices, I learned that this effect is best demonstrated between a passive pickup and an active DI box.
The interaction between a passive pickup and an active DI is often so vulnerable (primarily to capacitance changes) that swapping brands of cable can sound like EQ is being applied to the signal. In some cases the differences between cable brands are so stark that musicians will report dynamic changes to the ‘feel’ of their performance.
This explains why many professional guitar and bass players will match certain cable brands to the specific interaction of a particularly instrument + amplifier combination They are tuning their rigs with a cable, and the best cable for one rig, might not be the best for another.
On the opposite end of instrument performance is music mastering. In mastering, cable changes to either the analog transfer chain or monitoring chain are more subtle than between instruments and amplifiers. This is primarily due to the active balanced circuitry of both devices. Even so, many mastering and mix engineers report significant changes after simply swapping brands of cable, particularly in their monitoring path.
Could you achieve a great sounding mix or master using coat hangers as wires between all your gear? Absolutely, the electrons will flow and so will the music.
Could the results have sounded even truer to the source thru cabling that mitigates unwanted device interaction effects? According to my findings, and that of many other mastering engineers such as the esteemed Doug Sax, Bob Ludwig, Bernie Grundman and Greg Calbi, the answer is a resounding, YES.