Any active domain which is added in a hosting account has a number of records that enable 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 specific records created through the hosting company like 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 such as Voice-over-IP), and many others. With access to these records and by having the ability to edit them, you could have your web site with company A and your e-mails with company B, for instance. This gives you more independence as you can choose the best provider for every one of these services and you don't need to stick with one company. After you select a hosting company, you have to make certain that you can access all DNS records freely as some providers have an extra fee for this function.