Chances are your player is not full, but let me ask you this . . . Are you receiving this message on the screen?
“Not enough space for music DB. Please free 6 (or 90) mb.”
If you read this FAQ, you’ll see it’s a common issue, and has nothing to do with the memory capacity (or lack of it).
Formatting the player’s memory sets it back to the way it was when it was new, erasing all user-installed content in the process. It won’t affect your firmware (that runs the machine), so don’t worry about that. It’s in a hidden partition.
Formatting is only necessary when files get corrupted to the point where they’re too far gone (like if running ChkDsk in the linked FAQ doesn’t work), or if you want to clear the entire unit of music and start over. It’s not something you need to do unless it’s necessary. With your error mesage you may, or may not need to format it.
And they come formatted from the factory, so no, you didn’t need to do it when you first got it. 
