Each 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. For instance, the A record of a domain address is its IP address i.e. this record shows where the website is situated; the MX records reveal where the emails are stored, while using an SRV record you can use a domain for unconventional purposes, for instance a Voice-over-IP service. To be able to create and modify particular records enables you to have different services with different providers if, for illustration, your present host provides stable web hosting, but has problems with the email service, or you simply prefer to get a certain service from a certain company. Even though you must be able to create and edit these records freely and with no limits as you own a given domain, many companies charge extra to give you this option.