Every single 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 created manually if required. As an example, the A record of a domain name 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 through an SRV record you can use a domain for unconventional purposes, like a Voice-over-IP service. To be able to set up and modify certain records enables you to have different services with different providers if, for illustration, your current 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. While you must be able to create and modify these records freely and with no limitations as you own a given domain address, some companies charge extra to give you this option.
