Every domain which is registered and hosted has a lot of DNS records - some of them are created automatically when you host a domain, others can be set up manually if necessary. For example, the A record of a domain is its IP address i.e. this record reveals where the site is located; the MX records show where the e-mails are managed, while through an SRV record you can use a domain for unconventional purposes, like a Voice-over-IP service. To be able to create and modify particular records allows you to have different services with different companies if, for instance, your present host provides dependable web hosting, but has problems with the e-mail service, or you simply prefer to get a certain service from a particular company. Even though you can set up and edit these records freely and with no limitations as you own a given domain name, many companies charge extra to give you this option.