Any active domain name that's added in a hosting account has a variety of records which allow it to perform properly. In the common case, the name servers (NS records) show the location where the domain name is hosted and they are set on the side of the registrar company, but on the lower level there are particular records created through the hosting company such as A (IP address of the website/server), MX (e mail server), SRV (employing a domain address for non-website purposes on a certain port number like Voice-over-IP), etc. By having access to these records and by being in a position to modify them, you may have your web site with company A and your e-mails with company B, for instance. This gives you more independence as you can select the best provider for each of these services and you don't have to stick with only one company. After you select a hosting company, you have to make certain that you can access all DNS records freely as some companies have an extra fee for this feature.