When to Use a Separate Root Domain

If you have a single, primary site that has earned links,
 built content, and attracted brandattention and
awareness, it is very rarely advisable to place
any new content on a completely separate domain.
 There are rare occasions when this can make sense,
 and we’ll walk through these, as well as explain how
 singular sites benefit from collecting all of their
content in one root domain location.Splitting similar
or relevant content from your organization onto
 multiple domains can be likened to a store taking
American Express Gold cards and rejecting American Express
Corporate or American Express Blue—it is overly segmented
 and dangerous for the consumer mindset.

If you can serve web content from a singular domain,
 that domain will earn branding among the minds of
your visitors, references from them, links from other
 sites, and bookmarks from your regular customers.
 Switching to a new domain forces you to rebrand
 and to earn all of these positive metrics all over again.

There is a lot of debate about microsites, and although
 we generally recommend that you do not saddle yourself
 with the hassle of dealing with multiple sites and their
 SEO risks and disadvantages, it is important to
understand the arguments, if only a few, in favor of doing so