Rewriting the GNU Coreutils in Rust

Why should a utility that is I/O-bound and only uses minimal CPU time increase the CPU nice value? Such a utility should have a low CPU-nice value such that in case it needs the CPU (for a very short time) to issue the next IO operation it can do so and make the most efficient use of the available IO bandwidth. For other tasks it should not matter whether the few msec of CPU time needed are nice or non-nice, but for the utility it certainly matters whether it has to wait for the CPU or not.

And of course, high nice values are for background tasks where the user is not waiting for the output. If I run a core utility from the shell, I want to have the result now and I do not care whether a background task has to wait.