I agree. Most clients don't worry about technical details. "People don’t want a drill,they want a hole."

Add the documentation for the unusual parts in case some moron has to continue with the project six months later, and imagine that the moron is you, so be careful.

Somewhat related: "Don't Call Yourself A Programmer, And Other Career Advice" http://www.kalzumeus.com/2011/10/28/dont-call-yourself-a-pro... (I don't like the title, but I like the article.)