Any active domain name which is added in a hosting account features a number of records that permit it to function properly. In the typical case, the name servers (NS records) show the location where the domain is hosted and they're set on the side of the registrar company, but on the lower level there are certain records set through the hosting company like A (IP address of the website/server), MX (e mail server), SRV (employing a domain for non-website purposes on a particular port number like Voice-over-IP), etc. With access to these records and by having the ability to modify them, you could have your web site with company A and your e-mail messages with company B, for instance. This offers you more flexibility because you can pick the best provider for every one of these services and you don't need to stick to a single company. As soon as you select a hosting company, you have to make certain that you have access to all DNS records freely as some companies have an additional fee for this feature.