Each and every domain name 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 required. For example, the A record of a domain name is its IP address i.e. this record reveals where the site is situated; the MX records reveal where the emails are managed, while with an SRV record you can use a domain name for unconventional purposes, such as a Voice-over-IP service. To be able to create and modify specific records permits you to have different services with different providers if, for example, your current host provides good web hosting, but has problems with the email service, or you simply prefer to get a specific service from a certain company. Though you must be able to create and modify these records freely and without any limits as you own a given domain, many companies charge extra to give you this option.