Each domain name 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 created by hand if needed. For instance, the A record of a domain is its IP address i.e. this record reveals where the web site is located; the MX records reveal where the e-mails are stored, while with an SRV record you can use a domain for unconventional purposes, including a Voice-over-IP service. Being able to create and modify particular records permits you to have different services with different providers if, for illustration, your current host provides good web hosting, but has difficulties with the email service, or you simply prefer to get a particular service from a certain company. Even though you will be able to create and edit these records freely and without any restrictions as you own a given domain address, a lot of companies charge extra to give you this option.