You want to know the benefits of using resource (.resx) files.
Resource files provide a simple way to localize your .NET applications by automatically determining the .resx file to use based on a user’s locale. In addition, resource files provide a central location to store strings, files, and other scripts that can be referenced in a strongly-typed way. Another advantage is they can be compiled into satellite assemblies, making them easier to modify in a production environment.
String resources are great for error messages and user interface elements. Use them for human-readable text and not constants to be accessed programmatically.