Any active domain name that's added in a hosting account has a number of records that allow it to work properly. In the standard 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 certain records created 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 so on. By having access to these records and by having the capacity to edit them, you could have your site with company A and your e-mails with company B, for instance. This offers you more independence since you can pick the best provider for every one of these services and you do not have to stick to only one company. Whenever you select a hosting company, you have to make sure that you have access to all DNS records freely since some providers have an extra fee for this function.