Any active domain which is added in a hosting account has a variety of records that enable it to perform properly. In the standard 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 certain records created 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 particular port number such as Voice-over-IP), and many others. With access to these records and by being in a position to edit them, you may have your web site with company A and your emails with company B, for example. This offers you more overall flexibility because you can choose the best provider for every single one of these services and you don't have to stick with a single company. Whenever you select a hosting company, you have to make sure that you can access all DNS records freely because some companies have an additional fee for this feature.