The apps that automatically fill in tag information aren't always accurate. Besides, they come up with way too many genres: alternative rock, indie rock, alternative indie rock, indie alternative rock, indie alternative rock with a twist, etc. I prefer fewer genres (currently 48) that are meaningful to me and make it easier to find music by genre.
The same goes for lyrics. Many times, the lyrics that are automatically downloaded are inaccurate, including some that are for a completely different song or have garbage information instead of any lyrics. If you want it done right, do it yourself.
Another example is the "year" field. With compilation albums, especially, the year is meaningless to me. A "Best of" album that was released in 2008 may contain songs that were originally released in 1964. Rather than the year the compilation album was released, I want the year to reflect when that song originally came out (unless it was remade or performed live at a later date).
Finally, artwork. Most of the album art that's automatically downloaded is of low resolution. I prefer getting high-res artwork from sites like
AlbumArtExchange. All of this takes time and work (and it's still not finished), but the end result is far more appealing to me.
Currently:
Total songs in library: 27,918
Songs with no lyrics: 9,812
Songs with no year: 3,020
I wouldn't pay for a pre-formatted library, because it probably wouldn't be formatted using my criteria. I wouldn't pay extra for something I'd have to re-work anyway.