Not so much with the cables as what they make the equipment at the receiving end do. If the signal isn't delivered intact, or jitter is introduced, then the error correction systems in the digital to analogue converters have to work harder, which can affect the sound (or indeed the picture).
Optical cables - at least of the normal S/PDIF kind, with Toslink connectors, can sound worse than a direct electrical digital connection, as the signal must be converted from electrical to optical for transmission, and then back to electrical again at the receiving end. There's also some potential for reflections at the interface between the end of the optical 'cable' and the sender or receiver.
And yes I know about the 'digits is digits' argument and how a word file sent by email doesn't lose letters along the way, but digital audio and video is being sent and received and decoded in real time (or as near as possible). That's why error correction can be needed.
Some player manufacturers - Meridian is an example - use a read forward system, in which data is read from the disc, then dumped into a buffer, just to avoid the problems in real-time read/decode/convert systems.