Blueprint files are written in binary form and are usually edited visually. Still, they contain a whole set of useful information for the developers of the C++ part of the game:
There may be derived blueprint classes, which you can see by invoking Find Usages on a C++ class or when you're browsing your C++ code in the editor.
You can see the values of overridden properties.
You can navigate to the blueprint objects from your C++ code.