Any active domain name which is added in a hosting account has a number of records that allow it to function properly. In the standard case, the name servers (NS records) show where the 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 particular port number like Voice-over-IP), and many others. With access to these records and by having the capacity to edit them, you may have your web site with company A and your e-mails with company B, for illustration. This gives you more independence since you can choose the best provider for each of these services and you do not have to stick to only one company. When you select a hosting company, you have to make sure that you can access all DNS records freely as some companies have an extra fee for this feature.