Every single domain that is registered and hosted has lots of DNS records - some of them are set up automatically when you host a domain, others can be set up by hand if necessary. As an illustration, the A record of a domain is its IP address i.e. this record shows where the web site is situated; the MX records reveal where the e-mails are managed, while with an SRV record you can use a domain for unconventional purposes, like a Voice-over-IP service. Being able to create and modify particular records allows you to have different services with different companies if, for illustration, 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 certain company. While you must be able to create and edit these records freely and with no limits as you own a given domain name, a lot of companies charge extra to give you this option.