You should definitely hang on to them, since you still do need them to log in (to have them saved in your Member Information).

If you were to re-install the POL Viewer, without any backups, you would lose the saved settings and without the POL Password you would be rendered unable to access your account and re-setting the password(s) can be a tedious process indeed!

If you ever had to recover your account, the more information you can provide the Customer Service about it, the better.