What are the practical implications? The only one I can think of is if someone were trying to prove in court that you had a particular file.

A related question I've been wondering about is whether a hash or key+ciphertext are considered proof of possession of the original file. In theory an infinite number of files have the same hash, and the ciphertext could have been produced using a different key (or it could just be random data). In practice it's extremely unlikely (for sufficiently secure hash and encryption functions). What are the laws'/courts' views on cryptography?