IMHO, first of all, many of us already have the mp3 ordered by folders. And not being able to add them this way is quite annoying.
The second example is if you have a folder with i.e. a compilation:Instead of losing ages by editing the id3 album tags and so on, adding the folder is the fastest way.
another reason, is that at least for me, I still have a lot of mp3 downloaded from napster, and whit really messy id3 tags.
4: is quite annoying seeing your favorite artist's songs splitted in many different lists couse you have "audioslave", "Audioslave", and "AUDIOSLAVE". Lists grow exponentially when spaces/other simbols are involved (ie depeche-mode, or red hot chili peppers).
Last one is: someone just hate searching in DBs. And this is exactly the reason why I'm not using your app.