One function of the Access Edge Server is to provide remote access capabilities to a Lync Server infrastructure. After an internal deployment of pools is complete, an Access Edge Server can be provisioned to enable users to sign in and use their endpoints across the Internet.
As long as the appropriate SRV records exist in DNS or the client is manually configured correctly, a user can travel in and out of the office without ever making a change to an endpoint. This enables users to have full access to their internal features regardless of location.
Because 443 is a standard, well-known port, it is used for Remote Access by the Access Edge Service.