Each and every domain that is registered and hosted has lots of DNS records - some of them are created automatically when you host a domain, others can be set up by hand if needed. As an illustration, 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 managed, while with an SRV record you can use a domain name for unconventional purposes, like a Voice-over-IP service. Being able to set up and modify particular records enables you to have different services with different companies if, for example, your current host provides stable web hosting, but has troubles with the e-mail service, or you simply prefer to get a particular service from a specific company. Although you must 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.