Ease of testing is the most obvious benefit. A "pure" function is one whose result is simply based on its inputs, no dependency on external state/IO etc. Same

Ease of testing is the most obvious benefit. A "pure" function is one whose result is simply based on its inputs, no dependency on external state/IO etc. Same inputs, same outputs guaranteed. These types of functions, are really easy to reason about and unit test. State is often messy.