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