An audio cable carrying an unbalanced signal uses two wires: a signal and a ground.
The signal wire, as the name suggests, carries the audio signal to where it needs to go. The ground wire acts as a reference point for the signal. However, the ground wire itself also acts like an antenna, picking up unwanted noise along the way.
Because unbalanced cables can pick up noise as a signal is sent along the cable, they are more suitable for short distances, like connecting a guitar to a nearby amp. Doing so will minimize the risk for unwanted noise.