Every single domain that is 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 manually 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 handled, while using an SRV record you can use a domain name for unconventional purposes, such as a Voice-over-IP service. The ability to set up and modify specific records enables you to have different services with different companies if, for example, your current host provides stable web hosting, but has troubles with the e-mail service, or you simply prefer to get a certain service from a certain company. While you will be able to set up and edit these records freely and with no limits as you own a given domain address, some companies charge extra to give you this option.