Every single domain name that's registered and hosted has a lot of DNS records - some of them are created automatically when you host a domain, others can be set up by hand if needed. As an illustration, the A record of a domain name is its IP address i.e. this record shows where the website is situated; the MX records show where the e-mails are handled, while using an SRV record you can use a domain for unconventional purposes, such as a Voice-over-IP service. Being able to create and modify specific records permits you to have different services with different providers if, for instance, your present host provides stable web hosting, but has difficulties with the e-mail service, or you simply prefer to get a particular service from a certain company. Even though you can create and edit these records freely and with no limits as you own a given domain name, lots of companies charge extra to give you this option.