Any active domain name that's added in a hosting account features a number of records that enable it to function properly. In the general 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 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 certain port number such as Voice-over-IP), and so on. With access to these records and by being able to modify them, you could have your website with company A and your e-mails with company B, for instance. This offers you more freedom because you can pick the best provider for every one of these services and you don't have to stick to only one company. After you select a hosting company, you have to make sure that you have access to all DNS records freely since some providers have an additional fee for this feature.