Any active domain name that's added in a hosting account has a variety of records that permit it to perform properly. In the common case, the name servers (NS records) show where the Internet domain is hosted and they're set on the side of the registrar company, but on the lower level there are specific records set through the hosting company such as A (IP address of the website/server), MX (e mail server), SRV (employing a domain for non-website purposes on a specific port number like Voice-over-IP), and so on. With access to these records and by being in a position to modify them, you could have your web site with company A and your e-mail messages with company B, for example. This gives you more overall flexibility because you can choose the best provider for every single one of these services and you don't have to stick to a single company. When you choose a hosting company, you have to make sure that you can access all DNS records freely since some providers have an extra fee for this feature.