As long as your hard disk is already encrypted, you do not need to delete data on it as long as the decryption key remains private and protected.
Deletion by this method is far quicker than deletion using DBAN.
for Windows computers configured with bitlocker
For windows computers configured with bitlocker (see the related link on this page), the disk is effectively securely deleted/erased if you tamper with the computer casing, or if you use a BIOS command to change the bitlocker decryption code.
for Apple Macs configured with filevault
For Apple Mac computers configured with FileVault, the disk is effectively securely deleted/erased as long as the decryption key remains private.
Equally, it is a simple matter to change the FileVault password, as long as you know the current password, you can then easily change it to a new password (one that you do not need to remember).
Instructions for FileVault can be found folowing the Related link below.