Every domain that's registered and hosted has lots of DNS records - some of them are created automatically when you host a domain, others can be created manually if necessary. For example, the A record of a domain is its IP address i.e. this record reveals where the web site is situated; the MX records reveal where the e-mails are stored, while using an SRV record you can use a domain for unconventional purposes, such as a Voice-over-IP service. To be able to set up and modify particular records allows you to have different services with different providers if, for instance, your current host provides dependable web hosting, but has difficulties with the email service, or you simply prefer to get a specific service from a certain company. Even though you will be able to set up and edit these records freely and without any limitations as you own a given domain name, some companies charge extra to give you this option.