Every single 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 created by hand if necessary. For example, 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 managed, while using an SRV record you can use a domain name for unconventional purposes, including 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 stable web hosting, but has problems with the e-mail service, or you simply prefer to get a certain service from a particular company. Though you will be able to set up and edit these records freely and without any limits as you own a given domain, many companies charge extra to give you this option.