Every single domain that is registered and hosted has a great deal of DNS records - some of them are created automatically when you host a domain, others can be set up by hand if required. For example, the A record of a domain name is its IP address i.e. this record shows where the website is located; the MX records show where the e-mails are stored, while through an SRV record you can use a domain for unconventional purposes, including a Voice-over-IP service. To be able to create and modify particular records allows you to have different services with different providers if, for example, your present host provides stable web hosting, but has problems with the e-mail service, or you simply prefer to get a specific service from a specific company. Even though you will be able to set up and edit these records freely and without any limits as you own a given domain name, lots of companies charge extra to give you this option.