Scenarios where I can tamper with the password database, but not e.g. add a keylogger to your system are of course somewhat limited (although people love to put the database in sync services like Dropbox) Not just the passwords, the bigger data structure should be authenticated. Some possible scenarios:

I can copy the encrypted password to another entry that's easier to compromise: E.g. you might be suspicious of a phishing mail targetting your bank account, but are you paying the same attention to a faked message from a random webforum you use? (Or maybe an attacker can hack said forum a lot easier than your bank)

For a more featureful password manager that has gained a browser plugin that matches on URLs, I can now add an entry for my phishing URL to the password manager.