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It depends on how the content on secondary domains organized. If each secondary domain has a content theme, then it would be easier to get separate links for each of them and thus it benefits everyone. It helps user to quickly find/contribute what they are looking for, helps to attract different specific links and pass the value to primary.  If there is no such theme, then all those secondary domain will compete with each other  for mindshare, user contribution and attracting individual links which would make them to achieve high DA, I have similar setup. but instead of separate domains I have multiple subdomains with content categorized by theme. It helps may ways 1) Easier for single sign on. Use logged in one site does not need to log in again on anotyher site. 2) Can attract different types of links 3) easier for segmentation for advertisers.  Not all subdomains can achieve same DA or traffic but it helps overall network by internal linking.