Any active domain which is added in a hosting account has a variety of records that allow it to function properly. In the standard case, the name servers (NS records) show the location 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 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 specific port number like Voice-over-IP), and many others. Having access to these records and by being able to edit them, you can 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 choose the best provider for each of these services and you don't need to stick with a single company. Whenever you pick a hosting company, you have to make certain that you can access all DNS records freely as some providers have an extra fee for this function.