Every domain name that's registered and hosted has a lot of DNS records - some of them are created automatically when you host a domain, others can be created by hand if needed. As an illustration, the A record of a domain address is its IP address i.e. this record reveals where the web site is situated; the MX records reveal where the emails are handled, while through an SRV record you can use a domain for unconventional purposes, like a Voice-over-IP service. Being able to set up and modify specific records permits you to have different services with different companies if, for example, your present host provides good web hosting, but has troubles with the e-mail service, or you simply prefer to get a particular service from a certain company. Although you should be able to create and modify these records freely and without any limitations as you own a given domain name, some companies charge extra to give you this option.