Command Line – Piping File to a Command Without Piping Support

Use read -t 0 -N 0 to detect if data is available on stdin. Use test -t 0 or tty to try to detect if a pipe is connected to stdin.

It's useless in the sense that using it like that doesn't accomplish anything the other, possibly more efficient options can't (i.e. producing proper results).

But cat is way more powerful than just cat somefile. Consult man cat or read what I wrote in this answer. But if you absolutely positively only need the contents of a single file, you might get some performance advantage from not using cat to get at the file contents.

Regarding readability, this depends on your personal tastes. I like cating files into other commands for the same reason, especially if the performance aspects are negligible.

It also depends on what you're scripting. If it's your own shell and convenience methods for your desktop machine, nobody except you will care. If you stumble upon a case where the next tool in the chain would be better off being able to seek, and distribute this as a frequently used piece of software on some minimal Linux system on a low-performance router or similar device with real limits on processing ability, that's different. It always depends on the context.