Each and every domain that's registered and hosted has quite 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 address is its IP address i.e. this record shows where the website is situated; the MX records show where the e-mails are managed, while using an SRV record you can use a domain name for unconventional purposes, such as a Voice-over-IP service. Being able to create and modify specific records allows you to have different services with different companies if, for instance, your present host provides stable web hosting, but has difficulties with the email service, or you simply prefer to get a specific service from a specific company. Although you can set up and modify these records freely and without any limitations as you own a given domain address, many companies charge extra to give you this option.
