Every domain that is 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 by hand if required. For instance, the A record of a domain address is its IP address i.e. this record reveals where the website is located; the MX records show where the e-mails are managed, while through an SRV record you can use a domain for unconventional purposes, for instance a Voice-over-IP service. Being able to create and modify particular records enables you to have different services with different companies if, for example, 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. Even though you should be able to set up and modify these records freely and with no limits as you own a given domain name, many companies charge extra to give you this option.