> I've never seen anyone dig through VCS history to gain a better understanding of code.

I'm actually going through the ancient CVS history of Mozilla Firefox in order to learn about a relatively poorly understood piece of code that's still in there to this day:

http://mikeconley.ca/blog/2014/07/07/docshell-in-a-nutshell-...

and

http://mikeconley.ca/blog/2014/08/10/docshell-in-a-nutshell-...