Any active domain name that's added in a hosting account has a number of records that permit it to perform properly. In the general case, the name servers (NS records) show the location where the domain name 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 name for non-website purposes on a specific port number like Voice-over-IP), etc. With access to these records and by having the capacity to modify them, you can have your website with company A and your emails with company B, for illustration. This gives you more independence since you can pick the best provider for every single one of these services and you do not have to stick to one company. As soon as you select a hosting company, you have to make certain that you can access all DNS records freely since some providers have an additional fee for this function.