The question calls for a simple answer. White Label SEO is important because it benefits everyone involved: SEO agency, Reseller and, the client.
It allows SEO professionals to work efficiently without having to attract new clients now and then. The reseller gets to extend the services he offers with Search Engine Optimization, as a marketing agency. While the SEO professionals continue receiving new projects on a regular, the reselling company works on its key competencies without losing clients for lacking SEO services.