Most of the guitar players know that they can’t use a guitar amp speaker cable and guitar cords interchangeably, but they probably don’t know why. The main reason why you can’t do that is that these two cables are designed for two distinct purposes. Using one instead of the other can have adverse effects, from a simple annoying interference to equipment failure. Even the best bass guitar cable can’t do that, despite being heavier.
Although they have the same kind of connector, a ¼-inch plug, this is the only similarity between them. The instrument cable is low power, high impendence, as it is created to transform a weak signal from the guitar, to a boosted one in the amp.
The speaker cable is the opposite of that, having high power and low impedance, and it is built to convey a strong signal from the amp to the speakers, with high AC and voltage.