Ruff is a Python linter that is extremely fast, deriving its speed from Rust. Companies use linters to ensure that the codebase is as they like. And so, they code rules in linters to ensure they enforce the rules they want. Typically, linters are run on submitting pull requests or on committing when using pre-commit. If the time taken to run linters on each commit falls in the minutes range, which happens for big codebases, it becomes annoying.