Optimised team work
With the right processes and tooling, it becomes a lot easier to share code between developers. With the right amount of documentation in the right place, you also flatten the learning curve for onboarding developers to get up to speed. This reduces the risk that responsibility lies with a single developer (read: a single point of failure) and encourages developers to share, contribute, review and refactor code. Just make sure you have ample coverage so that you confidently can refactor, with minimal impact on existing features.
Any software project tends to grow in complexity over time. Without a good development strategy, sooner of later the quality of projects can erode.