Graham Charlton says, “Brands have sub-domains for a variety of reasons – to separate their sites for different audiences, to split their offerings, and so on. 

However, this can lead to conflict between the main and sub-domains if this strategy is not applied properly.

Before Google ended clustering in search results, this may well have worked well for brands, allowing them greater visibility insearch results.

In this post, I’ll show these sub-domain conflicts are affecting Ladbrokes, Coral, Oasis, ASOS and Barclay’s”.

How conflicts between sub-domains can harm your search rankings

‘Econsultancy’ Blog