Any active domain name that is added in a hosting account features a number of records which allow it to work properly. In the standard case, the name servers (NS records) show where the domain is hosted and they are set on the side of the registrar company, but on the lower level there are specific records set through the hosting company such as A (IP address of the website/server), MX (e-mail server), SRV (employing a domain address for non-website purposes on a particular port number like Voice-over-IP), and so on. Having access to these records and by being in a position to modify them, you can have your website with company A and your e-mails with company B, for illustration. This gives you more freedom as you can select the best provider for each of these services and you don't need to stick with a single company. As soon as you choose a hosting company, you have to make sure that you have access to all DNS records freely because some companies have an extra fee for this function.