There is no doubt that root domains are better for search engine results than subdomains, but can subdomains benefit you at all? I think so.
One reason you might want to use a subdomain for your search engine marketing and optimization for your product or service is because you have captured a search phrase and you are getting enough traffic for that phrase and a high enough search engine listing that you’ve realized it’s a valuable phrase. Google will only rank one page per domain for any particular keyword at one time. That pretty much locks you out of any future first page results for that same key phrase unless you do it on another property.
Since subdomains can often be seen by the search engines as an independent property from the root domain, you might consider going after that search phrase you’ve experience some success with as a subdomain to a viable root. If it is the case where you have a root domain ranking on page 1 for a search phrase, put your subdomain on a different root and go after the search phrase.
Another strategy to make this work is to create a subdomain on the same root domain, but make the subdomain a subniche within the one you are targeting. Make it specific and optimize the hell out of it. That subdomain can still rank for the original search phrase that your root domain captured and you’ll have two pages on Google for a specific keyphrase that you want to target.