Every single domain name that's 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 set up by hand if needed. As an example, the A record of a domain is its IP address i.e. this record shows where the website is located; the MX records show where the e-mails are managed, while with an SRV record you can use a domain name for unconventional purposes, such as a Voice-over-IP service. The ability to set up and modify certain records allows you to have different services with different companies if, for illustration, your current host provides good web hosting, but has issues with the email service, or you simply prefer to get a specific service from a particular company. While you will be able to create and modify these records freely and with no limitations as you own a given domain name, a lot of companies charge extra to give you this option.