Each domain name that 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 manually if required. As an example, the A record of a domain address is its IP address i.e. this record shows where the site is located; the MX records reveal where the emails are handled, while through an SRV record you can use a domain name for unconventional purposes, like a Voice-over-IP service. The ability to create and modify certain records allows you to have different services with different companies if, for example, your present host provides dependable web hosting, but has difficulties with the email service, or you simply prefer to get a certain service from a certain company. Although you should be able to set up and modify these records freely and with no limitations as you own a given domain, lots of companies charge extra to give you this option.