Any active domain which is added in a hosting account includes a number of records that allow it to function properly. In the standard 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 certain 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 particular port number such as Voice-over-IP), and many others. Having access to these records and by having the ability to modify them, you can have your website with company A and your emails with company B, for illustration. This gives you more independence because you can pick the best provider for every one of these services and you do not have to stick with one company. After you choose a hosting company, you have to make certain that you can access all DNS records freely because some providers have an extra fee for this feature.