Well, I am going to take the contrarian point of view.
I think the optimal length of I.C. cable is 1 meter.
(However, from a sonic standpoint, there certainly is nothing wrong with a half meter cable, unlike what your friend may have said!)
Another audiophile friend of mine passed on this same advice to me. "Never buy a 0.5 meter (20 inch) I.C."
His reasoning, and I agree, for the most part, is that there may come a time when due to system changes (and face it, we audiophiles are ALWAYS making system changes!), or changes to your rack, or how you position your equipment on your rack, you'll separate out the pieces of equipment you need to connect, and with only 20 inches of cable, you'll possibly run short. With 39 inches, you'll rarely encounter this problem, (Although, if you have a fair number of source components, like I do, you might. I have 5 input devices all going into my preamp. Obviously, 0.5 meter cables would not work for more than two of them.)
The cost of going from a half meter to a meter is not that great, IMHO. By having a bit more cable, you'll be able to separate your cables and keep proper distance between them. Plus by having all your cables at 1 meter, you'll be able to upgrade your cables and push your older (and usually more obsolete cables), to your lessor used components.
Anyway, my two cents worth!