Any active domain name that is added in a hosting account includes a number of records that allow it to work properly. In the common case, the name servers (NS records) show 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 a domain address for non-website purposes on a specific port number like Voice-over-IP), and so on. Having access to these records and by having the ability to edit them, you can have your website with company A and your emails with company B, for instance. This offers you more overall flexibility since you can choose the best provider for every single one of these services and you do not have to stick with one company. Whenever you select 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.