Any active domain name that's added in a hosting account has a variety of records that allow it to function properly. In the typical case, the name servers (NS records) show the location 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 (email server), SRV (using a domain for non-website purposes on a particular port number like Voice-over-IP), and many others. With access to these records and by being in a position to modify them, you may have your website with company A and your emails with company B, for example. 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. When you select a hosting company, you have to make certain that you have access to all DNS records freely as some companies have an additional fee for this feature.