Every domain that's registered and hosted has a great deal of DNS records - some of them are set up automatically when you host a domain, others can be set up manually if necessary. As an example, the A record of a domain is its IP address i.e. this record reveals where the site is located; the MX records show where the e-mails are handled, while through an SRV record you can use a domain name for unconventional purposes, like a Voice-over-IP service. To be able to set up and modify particular records permits you to have different services with different providers if, for illustration, your present host provides good web hosting, but has difficulties with the email service, or you simply prefer to get a specific service from a specific company. Although you will be able to set up and edit these records freely and without any limits as you own a given domain address, a lot of companies charge extra to give you this option.