[bumblebee]

...I can see no "purpose" behind hiding data. Not meaning any insult here, just curious is all...

Android provides different areas for an app to store its data. For instance for a game, the user does not need access to its sounds, graphics, user attained levels etc. other than from within the game.
MS gives you the choice. Internal, no user access, where all your interaction with the song files (and audio) is through its interface. It means you cannot inadvertently delete or rename a file behind the scenes. If you do this, MS will probably error when you want to view the song because it does not know what you have done.
When you create a new song or use the companion app or batch import, you can specify which storage area you want MS to store that song's data - page files, audio. Besides internal, you can select SD card which, although is still your tablet's internal memory, the OS provides you access to it (via a file manager for instance.)
Many tablets have external SD cards (like yours) so you can store songs there also (this saves your tablet's memory if you require it for other apps.) This needs to be set up in Options initially so MS knows how to find it in your specific tablet, but once this is done, you will be given this option when you create the song.
I use SD card generally. I use a file manager to name and organize the files, especially audio, where it resides in the same folder as the song it refers to (if I need to give it to someone else it is all in the one folder.) Then create the song leaving the files in the original location (it does not need to copy it anywhere, just reference them.)

I hope this helps