Any active domain name that is added in a hosting account features a number of records that permit it to perform properly. In the typical case, the name servers (NS records) show the location where the domain is hosted and they are set on the side of the registrar company, but on the lower level there are particular records created through the hosting company such as A (IP address of the website/server), MX (email server), SRV (using a domain address for non-website purposes on a particular port number such as Voice-over-IP), and many others. Having access to these records and by being able to edit them, you may have your site with company A and your e-mail messages with company B, for example. This gives you more freedom because you can select the best provider for every one of these services and you don't have to stick to one company. Whenever you select a hosting company, you have to make sure that you have access to all DNS records freely because some companies have an additional fee for this feature.