Any active domain which is added in a hosting account includes a variety of records that enable it to function properly. In the general case, the name servers (NS records) show where the domain name is hosted and they are set on the side of the registrar company, but on the lower level there are particular records created through the hosting company like A (IP address of the website/server), MX (email server), SRV (using a domain address for non-website purposes on a specific port number like Voice-over-IP), and many others. By having access to these records and by having the capacity to edit them, you may have your site with company A and your emails with company B, for instance. This gives you more independence since you can select the best provider for every one of these services and you do not have to stick to a single company. When you select a hosting company, you have to make certain that you can access all DNS records freely since some companies have an additional fee for this function.