One does not have to identify all uses, only one specific use--patent will still cover all uses.
Why do we care if it useful? What is the problem if there is no use?
- Might still cause backlog in the Patent Office
- Don't want to encourage invention of non-useful devices
- Not cost-free to grant patents to people
- Still leaves an opportunity to exploit system: and the more patents out there, the more would-be patent holders have to do to get new patent
What about the issue of "moral utility"? (Don't give patents for things that are bad for society.)
- But don't want PTO to be arbiter of morality!
- Plus even "illegal" activities can change over time (alcohol and Prohibition...)
- As a result: not looked to much in modern times, but concept still exists and PTO/courts may still look to it
- Does this matter? 96% of patents never make a penny!