Every domain name which is registered and hosted has lots of DNS records - some of them are created automatically when you host a domain, others can be set up manually if needed. As an example, the A record of a domain name is its IP address i.e. this record reveals where the web site is located; the MX records reveal where the emails are handled, while through an SRV record you can use a domain name for unconventional purposes, like a Voice-over-IP service. Being able to create and modify certain records allows you to have different services with different providers if, for illustration, your present host provides stable web hosting, but has issues with the e-mail service, or you simply prefer to get a specific service from a specific company. Even though you should be able to set up and modify these records freely and without any restrictions as you own a given domain address, a lot of companies charge extra to give you this option.