Any active domain name which is added in a hosting account features a number of records that enable it to function properly. In the typical case, the name servers (NS records) show the location where the 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 an Internet domain for non-website purposes on a particular port number like Voice-over-IP), and many others. With access to these records and by having the capacity to modify them, you can have your site with company A and your e-mail messages with company B, for instance. This offers you more flexibility as you can pick the best provider for every single one of these services and you don't have to stick to only one company. As soon as you pick a hosting company, you have to make certain that you can access all DNS records freely because some companies have an extra fee for this feature.