One of my pet peeves is "The Useless Use of cat Award". Someone awarded it to me as a teenager in the late 90s and I've been sore ever since.
Yup, it's often a waste of resources to run an extra 'cat'. It really demonstrates that you don't have the usage of the command receiving the output completely memorized. You know, the thousand or so commands you might be piping it into.
But, if you're doing a 'useless' use of cat, you're probably just doing it in an interactive session. You're not writing a script. (Or maybe you are, but even still, I bet that script isn't running thousands of times per second. And if it is, ok, time to question it).
So you're wasting a few clock cycles. The computer is doing a few billion of these per second? By the time you explain the 'useless' use of cat to someone, the time you wasted explaining to them why they are wrong, is greater than the total time that their lifetime usage of cat was going to waste.
There's a set of people who correct the same three pairs of homophones that get used incorrectly, but don't know what the word 'homophone' is. (Har har, they're/their/there). I always liken the people who are so quick to chew someone out for using cat, in the same batch of people who do this: what if I just want to use cat because it makes my command easier to edit? I can click up, warp to the front of the line, and change it real quick.
Sorry. I did say, it is a pet peeve.