Ok, here are some possible benefits over chihowa's proposal, for specific use cases.
- If the use case implies a system/"real" account rather than a virtual one (which I admit is a bad idea most of the time), the implementation practically comes for free: simply create an initially disabled account with a generated password. Particularly useful if the bunch of account creation doesn't actually use an e-mail account at all (say, university students accounts, with account names and initial passwords printed)
- You don't have to develop a different UI to differentiate account validation and regular password change.
- Some (web)mail applications are breaking URLs. Often times systems using generated URLs contain a link, plus a textual representation of the URL in case the link doesn't work (which usually means a text client), and sometimes some kind of pretty printer likes to add spaces after punctuation signs. With a short static URL and a password, you're minimizing copy/paste issues.