You'd be surprised. Especially if the testing environment is not readily available or if automated tests are not functional and comprehensive, large code changes can be the norm. A developer may habitually hang onto their code until a big chunk is complete, at which point it will take heaps of debugging to uncover where the errors are. This is why we need IaC to quickly create testing environments that closely mirror prod, and trunk-based development to ensure code changes are small and issues are caught as early as possible.