What are these entries in my Vault called 'Generated'?
These entries are created every time you use the Generate Passwords feature. This entry is created as a backup in case something goes wrong while creating an account or changing a password. For example, you may experience a timeout, forcing you to start the process over again.
Once you have succesfully created or changed your password on the webpage, LastPass will ask if you would like to confirm these changes. Once confirmed, LastPass will create a new entry or replace the old password, respectively.
The entry called 'Generated' will be automatically deleted from your Vault if LastPass detects the same domain and password somewhere else in your Vault. This is checked for whenever your login to that domain. If there is no repeated domain and password, it will remain in your Vault, unless deleted manually.