In most cases it doesn't matter. For me and my domain, some hosts on the domain point to my dynamic IP address at home. Perhaps www.domain.com points to the web host, access.domain.com points to my home dynamic IP and the MX record points to a 3rd parties mail servers.
If everything related to the domain is at the webhost, then there probably isn't a need for services like ZoneEdit.
If everything related to the domain is at the webhost, then there probably isn't a need for services like ZoneEdit.