Today, this is quite a funny system of load distribution, how many should you have after www, for example, Google?This is done solely for load balancing (add one server per subdomain) or geolocation (www1. for American visitors, www2 for European, etc.) purposes.
There's no benefit at all; it's probably even harming you. Since the subdomain is recognized as a separate website, your root domain won't benefit from it.