Every single domain that is registered and hosted has a lot of DNS records - some of them are set up automatically when you host a domain, others can be created manually if necessary. As an illustration, the A record of a domain address is its IP address i.e. this record reveals where the site is located; the MX records show where the emails are stored, while using an SRV record you can use a domain for unconventional purposes, like a Voice-over-IP service. The ability to create and modify specific records allows you to have different services with different companies if, for example, your present host provides stable web hosting, but has issues with the email service, or you simply prefer to get a specific service from a certain company. Even though you must be able to set up and edit these records freely and with no limitations as you own a given domain name, many companies charge extra to give you this option.