[OJFord]

Actually, this is exactly the sort of guide I've been meaning to read, since I'm inclined to take the opposite view.

Too often, I think, my task is probably sufficiently simple that it could be a nice portable obviously-a-script Bash script rather than Python/whatever.

[mannykannot]

Agreed. Bash (and similar scripts) are particularly useful in tasks involving filesystem and process management, where they offer capabilities that are more complicated in other languages. Functions are a helpful way to organize your use of those capabilities.