Each and every domain that is registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be created manually if needed. As an example, the A record of a domain address is its IP address i.e. this record reveals where the site is situated; the MX records reveal where the emails are managed, while through an SRV record you can use a domain address for unconventional purposes, like a Voice-over-IP service. To be able to create and modify particular records allows 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 particular service from a certain company. Although you must be able to create and modify 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.