Any active domain name that 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 where the domain name is hosted and they're set on the side of the registrar company, but on the lower level there are specific records created through the hosting company like 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), etc. Having access to these records and by having the ability to modify them, you may have your site with company A and your e-mail messages with company B, for illustration. This offers you more flexibility since you can select the best provider for each of these services and you don't need to stick with only one company. When you choose a hosting company, you have to make sure that you have access to all DNS records freely because some providers have an additional fee for this function.