In an ideal world, we'd never need to debug into library code... but there are times when it can be useful.

For example, trying to learn how React.NET loads or reloads .js files to understand its performance (and to fix project-specific caching issues). I'm debugging through my locally built .pdbs now, but it would be convenient to be able to just use what's in the NuGet package.

The only downside I've heard of beyond "you shouldn't need them!" is to keep your source code secure... but that's not really relevant for OSS right?