So, here we go again, another thread about bunch of people applying pseudoscience audiophile terms to Ethernet. Nope. Ethernet does not work that way. Ethernet, along with the TCP/IP stack are several layers of error detection and in some layers error correction. If an error is detected the frame, or packet, or datagram is discarded, or in the case of error correction, discarded and the retransmit requested.
So why fiber at all? Copper Ethernet cabling has limited range, 100ft is a safe bet, but depends on speed and cable standard.
but fiber for super short runs like 5ft is crazy waste of money.
Are you saying that bits of music are going to be retransmitted in a stream if an error occurs. I doubt it. I believe a BROADCAST protocol is used instead of the REQUEST/RESPONSE I think you are alluding to. Yes, I program this stuff.
The reason to use Fibre in audio is not for transmission length specifically but for Fibre's ability to stop analog noise from traversing the cable and getting into your DAC. It is very easy to test and more importantly to HEAR the difference.
What I hear with Fibre over Ethernet is improved clarity, especially when using my Benchmark gear, AHB2 + LA4.