To be honest, I’m not fully sure yet how to use the related items in the most meaningful way — at least not as long as I can’t get them to work reliably. ^^
I’m probably not using them the way @ben originally intended.
Especially the “author” field: I’m using it differently than it was designed. Because let’s be honest — as long as there’s no external online access and most projects only have one author anyway, the author field isn’t really needed in its classic sense.
Since the current Elements CMS setup allows filtering by tags, but not by categories, I simply repurposed the author field and turned it into my own category system. 
For your example, this would mean you could have “authors” like Rock & Pop, Classic Music, Jazz, etc.
This gives me additional and more flexible filtering options — even though the possibilities with related items are currently still quite limited.
Personally, I prefer using Collection Items, because the built-in filtering options give you much more control over what gets displayed.
Maybe the related items feature will be expanded in the future and allow filtering by categories as well.
Let’s wait and see … but first I need to fix my own related-items problem — which works randomly at best, and currently mostly doesn’t work.