Every single domain name which is registered and hosted has quite a lot of DNS records - some of them are set up automatically when you host a domain, others can be created by hand if needed. For example, the A record of a domain address is its IP address i.e. this record reveals where the web site is located; the MX records show where the e-mails are stored, while with an SRV record you can use a domain address for unconventional purposes, for instance a Voice-over-IP service. Being able to create and modify certain records enables you to have different services with different companies if, for illustration, your present host provides good web hosting, but has troubles with the email service, or you simply prefer to get a certain service from a certain company. While you must be able to set up and edit these records freely and with no restrictions as you own a given domain, many companies charge extra to give you this option.