Developers learn by example. This is no secret. The first advice given to new developers is to read a lot of good source code and the best advice given to experienced developers is to read a lot of good source code. Canonical texts for many languages let the source code say far more than the text. I’m thinking of text’s like Kernighan & Ritchie and Friedman & Felleisen.
When the world wide web was in its infancy view source was the best tool for wannabe webmasters learning their craft. Sure, bad designs and bad decisions propagated quickly. But good designs and good decisions propagated too. Those who really wanted to learn found best of breed web sites and quickly copied, edited and pasted their way to a beautiful site, learning much about web design in the process.
Is it worth it? Google serves billions of pages a day. Do you?