Any active domain which is added in a hosting account has a number of records which allow it to work properly. In the general 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 particular port number like Voice-over-IP), and many others. With access to these records and by having the capacity to modify them, you may have your website with company A and your emails with company B, for example. This offers you more independence because you can choose the best provider for every one of these services and you don't need to stick with a single company. After you pick a hosting company, you have to make sure that you can access all DNS records freely as some companies have an additional fee for this function.