1) I'd much rather have a function check a condition in a single place, than have 20 places in the code which check the same condition before calling it -- the

1) I'd much rather have a function check a condition in a single place, than have 20 places in the code which check the same condition before calling it -- the whole point of functions is to encapsulate repeated code to reduce bugs That's fine, but it's often a good idea to separate "do some work on a thing" and "maybe do work if we have a thing". Using the example in the article, it is sometimes useful to have multiple functions for those cases: fn frobnicate(walrus: Walrus) { ... } fn maybe_frobnicate(walrus: Option<Walrus>) { walrus.map(frobnicate) } But also… in languages like Rust, most of the time that second one isn't needed because of things like Option::map.