Each and every domain that is registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be set up by hand if necessary. For example, the A record of a domain name is its IP address i.e. this record shows where the web site is situated; the MX records reveal where the e-mails are handled, while through an SRV record you can use a domain address for unconventional purposes, such as a Voice-over-IP service. To be able to set up and modify certain records allows you to have different services with different providers if, for example, your present host provides good web hosting, but has difficulties with the email service, or you simply prefer to get a specific service from a specific company. Though you must be able to create and edit these records freely and with no restrictions as you own a given domain name, a lot of companies charge extra to give you this option.