Any active domain which is added in a hosting account has a number of records that enable it to work properly. In the typical case, the name servers (NS records) show the location where the domain name 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 name for non-website purposes on a specific port number such as Voice-over-IP), and many others. With access to these records and by being in a position to modify them, you can have your site with company A and your e-mail messages with company B, for example. This offers you more freedom since you can choose the best provider for every one of these services and you do not have to stick to only one company. Whenever you pick a hosting company, you have to make certain that you can access all DNS records freely as some companies have an additional fee for this function.