Any active domain that's added in a hosting account has a number of records that permit it to perform properly. In the common 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 specific records created through the hosting company like A (IP address of the website/server), MX (e-mail server), SRV (using an Internet domain for non-website purposes on a certain port number such as Voice-over-IP), and so on. 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 illustration. This offers you more overall flexibility because you can select the best provider for every one of these services and you don't have to stick to a single company. As soon as you choose a hosting company, you have to make sure that you have access to all DNS records freely since some companies have an additional fee for this feature.