Any active domain that's added in a hosting account features a variety of records that permit it to work properly. In the common case, the name servers (NS records) show where the domain name is hosted and they are set on the side of the registrar company, but on the lower level there are specific records created through the hosting company like A (IP address of the website/server), MX (email server), SRV (employing a domain address for non-website purposes on a certain port number like Voice-over-IP), and so on. By having access to these records and by being able to edit them, you could have your web site with company A and your e-mails with company B, for instance. This offers you more overall flexibility because you can pick the best provider for every single one of these services and you do not have to stick to a single company. When you select a hosting company, you have to make sure that you have access to all DNS records freely because some providers have an extra fee for this feature.