Any active domain that's added in a hosting account features a variety of records that enable it to function properly. In the general case, the name servers (NS records) show the location where the Internet domain is hosted and they're set on the side of the registrar company, but on the lower level there are particular records created through the hosting company such as A (IP address of the website/server), MX (email server), SRV (employing a domain name for non-website purposes on a certain port number like Voice-over-IP), and many others. By having access to these records and by being in a position to modify them, you could have your website with company A and your emails with company B, for instance. This offers you more independence as you can select the best provider for every single one of these services and you don't have to stick to only one company. After you choose a hosting company, you have to make sure that you can access all DNS records freely since some companies have an extra fee for this feature.