Any active domain that's added in a hosting account has a variety of records that permit it to function properly. In the common case, the name servers (NS records) show the location 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 set through the hosting company like A (IP address of the website/server), MX (e-mail server), SRV (employing a domain address for non-website purposes on a specific port number such as Voice-over-IP), and so on. Having access to these records and by having the ability to modify them, you may have your website with company A and your e-mail messages with company B, for instance. This offers you more independence as you can select the best provider for every single one of these services and you don't need to stick with a single company. When you choose a hosting company, you have to make sure that you have access to all DNS records freely as some providers have an extra fee for this function.