That is a particularly useful approach in functional languages, where the function declaration itself is actually a fairly concrete guarantee of what the function will do.

Shell scripts are almost the complete opposite end of the spectrum:

Shell script functions are usually only created as a last resort.

Global side effects (creating temporary files, changing global system state, global variables, etc.) are what shell scripts are all about.

There are rare snippets of shell scripting that are different, using local variables and doing some sort of calculation, but that is the exception, not the rule.

While ideally comments would be prolific, poetic, and perfect, some commenting is always better than none and most developers have bad habits of not commenting their code, so pushing them gently in the direction of more, not less, usually works.