Any active domain name that is added in a hosting account has a number of records that allow it to function properly. In the typical case, the name servers (NS records) show the location 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 created through the hosting company such as A (IP address of the website/server), MX (e mail server), SRV (employing a domain for non-website purposes on a particular port number like Voice-over-IP), and so on. Having access to these records and by being in a position to edit them, you could have your site with company A and your emails with company B, for example. This gives you more overall flexibility because you can choose the best provider for each of these services and you don't have to stick to only one company. As soon as you choose a hosting company, you have to make certain that you have access to all DNS records freely as some providers have an extra fee for this feature.