Knowing password length makes it easier to crack an insecure password.

The SHA256 hash of a 6-symbol diceware password, where each symbol has its first letter capitalized and the rest lowercase, with 1! appended for compliance with misguided composition rules is 540b5417b5ecb522715fd4bb30f412912038900bd4ba949ea6130c8cb3c16012. There are 37 octets in the password. You know the length. You know the composition rules. You have an unsalted hash. It's only 77 or so bits of entropy. Get cracking, I'll wait.