Each domain that is registered and hosted has 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 name is its IP address i.e. this record reveals 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 for unconventional purposes, for instance a Voice-over-IP service. The ability to create and modify particular records permits you to have different services with different providers if, for example, your current host provides stable web hosting, but has issues with the email service, or you simply prefer to get a specific service from a specific company. While you will be able to create and modify these records freely and without any limits as you own a given domain, some companies charge extra to give you this option.