I inherited management of an AD forest some time ago, and as there were never any issues with authentication or other AD-dependent services (which weren't operator error), I never made any changes. The site arrangement is now in flux as we're migrating out of one of our data centers.
We have multiple child domains off the forest root. They're all co-located physically in the same site, and will be moving forward, with the root domain. The previous administrator set up separate AD sites for each child domain. The child domains have their own subnets, and these are associated with the domain-specific sites.
In other words, we have these AD sites:
Location1-rootDomain
Location1-ChildDomain1
Location1-ChildDomain2
Location2-rootDomain
Location2-ChildDomain1
and so forth. I believe the thinking was this was somehow supposed to prevent root clients from authenticating against child DCs, or something. I really don't see the purpose. I only see it as unnecessarily delaying replication among different-domain DCs in the same physical location.
Is there any valid reason not to consolidate AD sites and put all the DCs in the same location in the same AD site? We only do TS licensing in the root domain, and we don't have software dependent on site (aside from Exchange, where nothing will be moving anyway).