For more security: overwrite empty disk space

I know it might seem a stupid question but I haven't come across any forum or post on the internet about:

- What does "overwriting an empty disk space" mean/do?

- Why doing that makes it more secure when encrypting a disk?

Thanks in advance.

Solution 1:

-I don't have the rep to comment-

Overwriting unused disk space means that data is written to areas of the disk that are not currently being used by a file. Overwriting unused disk space makes it more difficult to recover deleted files (yes they are still there after being deleted, even after the recycling bin is emptied).

Overwriting unused disk space in an encrypted disk is more secure because if unauthorized access is gained to the encrypted disk, the data that was not overwritten is easily recoverable.

Solution 2:

• Overwriting empty disk space means to overwrite the space in a disk not in use by the file system, with either random content or zeros.

• The reason is to make the data which still might be recoverable in this area practically irrecoverable.