Digital cable length- SPDIF vs AES/EBU- 1.5 meter for either?

Sorry, just saw this thread. Are you all saying any coax digital cable that is not 1.5m long should be tossed out? Why are they even manufacturing cables that are in different (from 1.5m) lengths?

Al, thanks as always for the thorough explanation. I saw the references to the comparisons between 1.0m and 1.5m cable lengths but was left with the impression that longer lengths were not desirable, all things considered and being equal. To your point, I find it difficult to believe a single length could be optimal in all circumstances given all the other variables, including the cable material and construction techniques.