Every domain name that 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 by hand if necessary. As an example, the A record of a domain name is its IP address i.e. this record shows where the site is located; the MX records reveal where the emails are managed, while using an SRV record you can use a domain name for unconventional purposes, including a Voice-over-IP service. The ability to create and modify certain records permits you to have different services with different companies if, for illustration, your current host provides good web hosting, but has difficulties with the email service, or you simply prefer to get a certain service from a particular company. While you will be able to set up and modify these records freely and with no restrictions as you own a given domain, many companies charge extra to give you this option.