Any active domain name that's added in a hosting account includes a variety of records that permit it to perform properly. In the general case, the name servers (NS records) show the location where the domain name is hosted and they are set on the side of the registrar company, but on the lower level there are particular 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 certain port number such as Voice-over-IP), and many others. Having access to these records and by having the capacity to edit them, you may have your site with company A and your emails with company B, for example. This gives you more freedom as you can pick the best provider for each of these services and you do not have to stick with a single company. When you choose a hosting company, you have to make sure that you can access all DNS records freely because some companies have an additional fee for this function.