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