Any active domain name that's added in a hosting account has a variety of records that enable it to perform properly. In the general case, the name servers (NS records) show the location where the domain is hosted and they're set on the side of the registrar company, but on the lower level there are particular records created through the hosting company like A (IP address of the website/server), MX (e-mail server), SRV (using a domain for non-website purposes on a particular port number like Voice-over-IP), and many others. By having access to these records and by having the ability to modify them, you may have your web site with company A and your e-mail messages with company B, for example. This gives you more flexibility as you can select the best provider for each of these services and you do not have to stick with one company. After you pick a hosting company, you have to make sure that you can access all DNS records freely as some providers have an extra fee for this feature.