Developers spend a fair chunk of time during their development flow on fixing relatively trivial problems in their code. pre-commit.ci both enforces that these issues are discovered (which is opt-in for each developer's workflow via pre-commit) but also fixes the issues automatically, letting developers focus their time on more valuable problems.

configuration: zero configuration setup -- nothing is needed beyond the .pre-commit-config.yaml file you already have!

auto fixing pull requests: if tools make changes to files during a pull request, pre-commit.ci will automatically fix the pull request.

speed: much faster than comparable, free CI systems

caching: tool caching is baked in and shared across all users. this means that the more users there are of pre-commit.ci, the more likely you will get faster builds!

automatic updates: pre-commit.ci will periodically autoupdate your configuration ensuring that your hook versions are kept up to date.