Unlocking your files is when, for example, you submit WAV files to a project, the project owner can download the WAV version. If they are locked, the project owner can only download the lower quality version of the file (the mp3).
You would need to have your files unlocked if, for example, you created a project where you were looking for a track to be remixed by other members. They’d need to download the highest quality version of your music in order to create a remix that is high quality.
However, if you haven’t unlocked your files and the project owner requires a WAV version, the project owner will contact you for this, so it’s not something you need to worry about!