I think 5.b is mostly applicable when you're packaging DLLs. I don't see much use for it in internal projects (Eg. If I'm building a end user solution and not developer solution).
Yes - it's mostly applicable when you're creating APIs and developer solutions. But even in case of internal tools/ exes, you might need to share functionality with a internal partner team and it's helpful if they don't have to read code they don't need to use.