Every domain name which is registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be created manually if necessary. For instance, 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 using an SRV record you can use a domain name for unconventional purposes, such as a Voice-over-IP service. To be able to create and modify certain records enables you to have different services with different providers if, for illustration, your present host provides good web hosting, but has troubles with the email service, or you simply prefer to get a specific service from a particular company. While you must be able to set up and modify these records freely and with no limitations as you own a given domain name, many companies charge extra to give you this option.