Any active domain name that's added in a hosting account includes a variety of records that allow it to function properly. In the general case, the name servers (NS records) show the location where the Internet domain is hosted and they are set on the side of the registrar company, but on the lower level there are particular records set through the hosting company such as A (IP address of the website/server), MX (e mail server), SRV (using a domain name for non-website purposes on a certain port number like Voice-over-IP), etc. Having access to these records and by having the ability to modify them, you could have your website 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 to only one company. After you select 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 feature.