Any active domain that's added in a hosting account has a variety of records that enable it to function properly. In the typical case, the name servers (NS records) show where the Internet domain is hosted and they are set on the side of the registrar company, but on the lower level there are specific records created through the hosting company such as A (IP address of the website/server), MX (e-mail server), SRV (using a domain address for non-website purposes on a particular port number such as Voice-over-IP), and so on. By having access to these records and by having the ability to modify them, you may have your site with company A and your emails with company B, for illustration. This offers you more independence since you can pick the best provider for every single one of these services and you don't need to stick with a single company. Whenever you select a hosting company, you have to make certain that you have access to all DNS records freely as some providers have an extra fee for this function.