In academia, it's considered cheating if a student copies code/work from someone/somewhere else without giving credit, and tries to pass it off as his/her own.

Should companies make it a requirement for developers to properly credit all non-trivial code and work that they did not produce themselves? Is it useful to do so, or is it simply overkill?

I understand there are various free licenses out there, but if I find stuff I like and actually use, I really feel compelled to give credit via comment in code even if it's not required by the license (or lack thereof one).