Every single domain which is registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be set up manually if required. As an 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 through an SRV record you can use a domain for unconventional purposes, like a Voice-over-IP service. To be able to set up and modify certain records permits you to have different services with different companies if, for example, your current host provides stable web hosting, but has issues with the email service, or you simply prefer to get a particular service from a particular company. Even though you should be able to set up and edit these records freely and with no limitations as you own a given domain, a lot of companies charge extra to give you this option.