You couldn't share that source code with your friends, unless they were Unix licensees too, or build binaries from it and do whatever you wanted with them. Reading Unix source code was eye-opening. That experience gave me the confidence to write my own Unix utilities. Reading any kind of source code will teach you something. Just don't confuse it with open source, which also has other properties.
Source code is a great thing.
I'm leading a lawsuit to verify that the First Amendment protects our right to publish source code, or communicate it privately with others. IBM mainframe OS's had something much closer to open source. They used to publish the source code on tapes and microfilm, and give it to anyone who ordered it. The idea was that it was useless to you unless you had an IBM mainframe. That idea went by the wayside when Amdahl and Fujitsu and etc started building IBM 370 clones, and they locked up the software.