Sometimes it comes down to having a third party service handle support or provide the framework, so adding it as a subdomain makes it easier to integrate into y

Sometimes it comes down to having a third party service handle support or provide the framework, so adding it as a subdomain makes it easier to integrate into your site. And Google often treats subdomains as their own site so you can have a well structured support driven layout, rather than a site trying to showcase featured content while battling with support content.