Each and every domain which is registered and hosted has quite a lot of DNS records - some of them are created automatically when you host a domain, others can be created manually if needed. As an illustration, the A record of a domain is its IP address i.e. this record shows where the web site is situated; the MX records show where the emails are managed, while through an SRV record you can use a domain name for unconventional purposes, like a Voice-over-IP service. Being able to create and modify specific records allows you to have different services with different providers if, for instance, your current host provides stable web hosting, but has issues with the email service, or you simply prefer to get a certain service from a certain company. Though you should be able to set up and edit these records freely and without any limits as you own a given domain, lots of companies charge extra to give you this option.