Any active domain that's added in a hosting account includes a number of records that allow it to function properly. In the general case, the name servers (NS records) show where the Internet 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 specific port number such as Voice-over-IP), and so on. By having access to these records and by having the capacity to modify them, you could have your website with company A and your e-mails with company B, for instance. This gives you more independence as you can select the best provider for every one of these services and you don't need to stick with one company. Whenever you choose a hosting company, you have to make certain that you have access to all DNS records freely since some providers have an additional fee for this feature.