Disable new disks requests for Time Machine

If you don’t use Time Machine, you might notice that every time you attach a empty hard disk to your Mac, you get asked if you want to use this hard disk Time Machine backups. Disable this dialog box with the following command:

defaults write com.apple.TimeMachine DoNotOfferNewDisksForBackup -bool true

Restart your Mac or log out and back in again for the changes to take effect.

Revert to defaults setting:

defaults delete com.apple.TimeMachine DoNotOfferNewDisksForBackup