Any active domain that's added in a hosting account has a number of records which allow it to perform properly. In the standard case, the name servers (NS records) show the location where the Internet domain is hosted and they're 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 (e-mail server), SRV (using a domain address for non-website purposes on a specific port number such as Voice-over-IP), and many others. Having access to these records and by being in a position to modify them, you could have your website with company A and your e-mail messages with company B, for instance. This gives you more flexibility since you can select the best provider for every single one of these services and you don't need to stick with only one company. Whenever you select a hosting company, you have to make certain that you can access all DNS records freely since some companies have an extra fee for this function.