There are dubious benefits. I use Emacs all the time, and have made a few contributions to it, but I won't be digging into the core C code anytime soon. First

There are dubious benefits. I use Emacs all the time, and have made a few contributions to it, but I won't be digging into the core C code anytime soon. First, learning enough to fix even a simple problem takes quite a bit of time. Second, the lessons learned will be mostly about Emacs, and not generally applicable; that's the way things are with most big programs. The amount of time required to meaningfully learn from or contribute to something as hairy as a web browser or compiler is large enough that you can only engage with a few. Personally, I never want to have to look at my web browser's source code.