Codebook 4 removes the Backups feature, which is now obsolete. In previous versions of Codebook for macOS and Windows this feature would make a full (encrypted) backup copy of your database before any change to the Master Password, as well as before any sync operation (if enabled in Preferences). Since these backup files are no longer needed and cannot be used anymore, Codebook 4 offers to remove them for your computer. This is entirely optional, but we recommend it as Codebook's internal encryption has been updated to be much stronger than was used for these backup files, and it's never a good idea to leave old, sensitive information laying around!