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