Any active domain that's added in a hosting account has a variety of records that enable it to function properly. In the typical case, the name servers (NS records) show where the domain name is hosted and they are set on the side of the registrar company, but on the lower level there are certain records set through the hosting company like A (IP address of the website/server), MX (email server), SRV (employing a domain for non-website purposes on a specific port number like Voice-over-IP), and many others. With access to these records and by being in a position to edit them, you may have your web site with company A and your e-mail messages with company B, for example. This offers you more freedom because you can choose the best provider for each of these services and you do not have to stick to only one company. As soon as you pick a hosting company, you have to make sure that you can access all DNS records freely because some companies have an additional fee for this feature.