Any active domain name which is added in a hosting account includes a number of records that allow it to perform properly. In the general case, the name servers (NS records) show the location 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 set through the hosting company such as A (IP address of the website/server), MX (e mail server), SRV (using a domain for non-website purposes on a certain port number like Voice-over-IP), and so on. With access to these records and by being able to modify them, you could have your site with company A and your e-mail messages with company B, for illustration. This offers you more flexibility since you can pick the best provider for every one of these services and you do not have to stick to only one company. After you choose a hosting company, you have to make sure that you have access to all DNS records freely since some companies have an extra fee for this feature.