Any active domain name which is added in a hosting account has a number of records that allow it to work properly. In the general case, the name servers (NS records) show the location where the Internet domain is hosted and they're set on the side of the registrar company, but on the lower level there are certain records created through the hosting company like A (IP address of the website/server), MX (e mail server), SRV (using a domain address for non-website purposes on a particular port number like Voice-over-IP), and so on. With access to these records and by being in a position to edit them, you may have your site with company A and your emails with company B, for instance. This gives you more overall flexibility since you can select the best provider for every one of these services and you do not have to stick with a single company. After you select 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 function.