Any active domain that is added in a hosting account includes a number of records which allow it to work properly. In the typical case, the name servers (NS records) show where the Internet 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 certain port number like Voice-over-IP), and many others. With access to these records and by having the ability to modify them, you could have your web site with company A and your e-mails with company B, for illustration. This offers you more independence since you can select the best provider for every single one of these services and you do not have to stick to one company. Whenever you choose 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.