Any active domain name which is added in a hosting account features a variety of records which allow it to function properly. In the standard case, the name servers (NS records) show the location where the domain is hosted and they're set on the side of the registrar company, but on the lower level there are certain records set through the hosting company like A (IP address of the website/server), MX (e mail server), SRV (employing a domain for non-website purposes on a specific port number such as Voice-over-IP), and so on. With 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 gives you more flexibility as you can pick the best provider for every single one of these services and you don't need to stick to a single company. After you choose a hosting company, you have to make certain that you can access all DNS records freely since some companies have an additional fee for this feature.