Each domain name that is registered and hosted has lots of DNS records - some of them are created automatically when you host a domain, others can be set up manually if required. As an example, the A record of a domain address is its IP address i.e. this record reveals where the website is located; the MX records reveal where the e-mails are managed, 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 allows you to have different services with different companies if, for example, your current host provides dependable web hosting, but has issues with the email service, or you simply prefer to get a particular service from a particular company. Though you must be able to create and modify these records freely and without any limitations as you own a given domain address, some companies charge extra to give you this option.