Any active domain that's added in a hosting account includes a number of records that allow it to work properly. In the typical case, the name servers (NS records) show the location where the domain name is hosted and they're 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 an Internet domain for non-website purposes on a particular port number such as Voice-over-IP), and many others. Having access to these records and by being able to edit them, you may have your site with company A and your emails with company B, for illustration. This offers you more flexibility because you can select the best provider for each of these services and you do not have to stick with a single company. When you select a hosting company, you have to make sure that you can access all DNS records freely as some companies have an extra fee for this function.