While cat could be argued to be overkill (... but not by me...), that's not a useless use of cat because if you pull it out (as you've done) there's nothing to

While cat could be argued to be overkill (... but not by me...), that's not a useless use of cat because if you pull it out (as you've done) there's nothing to actually read the bytes from stdin and write them to stdout. All you've done is opened two files and closed them again. (Edited to add: unless you're using zsh, apparently)