ну там конкретно написано
We advocate for a system focused on pushing workflow integration as early as possible. When possible, checks are enabled as compiler errors. To avoid breaking builds, tool writers take on the task of first fixing all the existing issues in the codebase, allowing us to "ratchet" the quality of Google's codebase one small step at a time, without regressions. Since we present the errors in the compiler, developers encounter them immediately after writing code, while they are still amenable to making changes.