Genre tags are important for me, because that’s one of the few keywords I am making playlists from. And that’s why I am interested in having more than just the generic “Rock” entry there. Audirvaña doesn’t support multiple Genre fields but if it finds them, it shows them as it was just one field.
The English/American wikipedia tries to keep track on the ID3 tags: https://en.wikipedia.org/wiki/ID3
When I buy digital music, the Genre tag quite often is empty. I guess nobody wants to burn their fingers here, as it really is also a personal taste. I always look at Discogs for the music genre and msuic style, but do not agree with every assignment someone did there. But at least they try.