Automatic site coverage in AD

Usually domain controllers (DCs) register site-specific records for their local site in DNS, enabling clients to easily find DCs and other services that are closest to them. If a site contains no DCs, then DCs in the sites closest to that site (calculated by site-link costs) will register site-specific records for that site as well, to help clients find a DC as close as possible. This is known as automatic site coverage

AutoSiteCoverage enabled, DCs in nearby sites (determined by site link costs) will dynamically register themselves as referral sources for the site without DCs.

Benefits:

Ensures clients in sites without DCs can still authenticate and access domain resources.
Improves overall network performance by directing clients to the closest available DC.