Any active domain name that is added in a hosting account has a number of records that enable it to perform properly. In the typical 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 specific records set 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 certain port number such as Voice-over-IP), and many others. Having access to these records and by having the ability to edit them, you could have your web site with company A and your e-mails with company B, for illustration. This gives you more overall flexibility since you can select the best provider for every single one of these services and you don't have to stick with a single company. After you choose a hosting company, you have to make sure that you have access to all DNS records freely because some providers have an extra fee for this function.