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You could fix bugs in Laravel and develop new features in the framework/library and test them locally before you create the PR you are about to send. The most common one is maintaining your own fork of a third party library. If you are using a certain library for your project and you decide to change something in the library, you will want your project to use the patched version. If the library is on GitHub, you can simply fork it there and push your changes to your fork. After that, you update the project’s composer.json.