Remote File Plugin tries to find matching branch in repository which defined in Plugin SCM definition with in the Branch Sources SCM definition.
By this, Jenkins Files will be used in the branch of Jenkins File repository which have the same branch name in code source repository.
Branch Specifier will be ignored if this options is checked.
If plugin can not find same branch name in the Jenkins File repository, it will automatically fall back to branch, which is defined in below "Fallback Branch" field (default is master), and will search for Jenkins file in it.
This feature only work for Git SCM definitions