I agree though that its hard to find use cases for forks in a typical business- however Unreal Engine would be a great example of it where the private repositor

I agree though that its hard to find use cases for forks in a typical business- however Unreal Engine would be a great example of it where the private repository is shared by multiple development teams. If you have access to it (because you've agreed to the Source License), you can make a private fork and send in a PR to the main repository. Epic probably won't merge it though unless you represent a big studio.