Any active domain name which is added in a hosting account features a variety of records that enable it to perform properly. In the standard case, the name servers (NS records) show 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 set through the hosting company such as A (IP address of the website/server), MX (email server), SRV (using an Internet domain for non-website purposes on a certain port number like Voice-over-IP), etc. Having access to these records and by being able to modify them, you can have your site with company A and your e-mails with company B, for instance. This offers you more overall flexibility as you can select the best provider for every one of these services and you do not have to stick with a single company. Whenever you choose a hosting company, you have to make certain that you have access to all DNS records freely since some companies have an extra fee for this feature.