Any active domain that is added in a hosting account features a number of records that allow it to work properly. In the common 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 set through the hosting company like A (IP address of the website/server), MX (e mail server), SRV (employing a domain name for non-website purposes on a specific port number like Voice-over-IP), etc. By having access to these records and by having the capacity to edit them, you may have your site with company A and your e-mail messages with company B, for illustration. This gives you more overall flexibility because you can select the best provider for each of these services and you don't need to stick to one company. After you select a hosting company, you have to make certain that you can access all DNS records freely because some companies have an extra fee for this feature.