Every single domain name that's registered and hosted has quite a lot of DNS records - some of them are set up automatically when you host a domain, others can be created by hand if necessary. For example, the A record of a domain address is its IP address i.e. this record shows where the website is located; the MX records show where the e-mails are handled, while with an SRV record you can use a domain name for unconventional purposes, for instance a Voice-over-IP service. The ability to set up and modify particular records permits you to have different services with different providers if, for example, your present host provides stable web hosting, but has difficulties with the email service, or you simply prefer to get a particular service from a particular company. Although you will be able to create and edit these records freely and without any limitations as you own a given domain, many companies charge extra to give you this option.