Every domain name that's registered and hosted has quite a lot of DNS records - some of them are created automatically when you host a domain, others can be created manually if needed. For example, the A record of a domain address is its IP address i.e. this record shows where the website is located; the MX records reveal where the e-mails are stored, while with an SRV record you can use a domain for unconventional purposes, such as a Voice-over-IP service. The ability to set up and modify certain records permits you to have different services with different providers if, for instance, your current host provides stable web hosting, but has issues with the e-mail service, or you simply prefer to get a certain service from a particular company. Even though you can set up and edit these records freely and without any restrictions as you own a given domain, a lot of companies charge extra to give you this option.