Hi Ivan!

From my exprience there are multiple reasons - The main one: I've learned tons from reading code. The ability to jump into code that does X to see how it's implemented is worth a lot to me. This is something I love about the jvm ecosystem which is unfortunately not present in many other languages. - Many libraries/frameworks (Spring Data comes to mind) provide very leaky abstractions. Understanding how the underlying technology is used can make a big difference. - Address questions when the documentation is not clear enough. - And last: to discover bugs in libraries. This is not common, but it happens.