Every single domain name which is registered and hosted has a great deal of DNS records - some of them are set up automatically when you host a domain, others can be set up by hand if necessary. As an illustration, the A record of a domain address is its IP address i.e. this record shows where the site is located; the MX records reveal where the e-mails are stored, while with an SRV record you can use a domain name for unconventional purposes, including a Voice-over-IP service. The ability to set up and modify particular records allows you to have different services with different companies if, for instance, your present host provides stable web hosting, but has troubles with the e-mail service, or you simply prefer to get a specific service from a certain company. Though you must be able to create and modify these records freely and with no restrictions as you own a given domain name, some companies charge extra to give you this option.