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