Prevention is better than cure. The very crux of software development is to establish monitoring and inspection processes at each stage of its life cycle.
Fixing an error is the cheapest during the development stage, which gets progressively expensive with each stage and is the most expensive in the post-release maintenance phase. A code review tool automates the code inspection and monitoring process.
It is a major component in Continuous Integration (CI) which helps in keeping the code in its functional state. Before CI appeared, developers used to write thousands of lines of code, and then integrate them. The process of integration was prone to errors, tedious, and challenging.