Each and every domain name that's registered and hosted has a great deal of DNS records - some of them are created automatically when you host a domain, others can be created manually if required. As an 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 e-mails are managed, while using an SRV record you can use a domain name for unconventional purposes, like a Voice-over-IP service. Being able to set up and modify certain records allows you to have different services with different providers if, for example, your current host provides good web hosting, but has troubles with the email service, or you simply prefer to get a particular service from a specific company. Though you will be able to create and modify these records freely and without any limitations as you own a given domain, some companies charge extra to give you this option.