Every domain 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 created by hand if required. For example, the A record of a domain address is its IP address i.e. this record reveals where the site is situated; the MX records show where the emails are managed, while with an SRV record you can use a domain for unconventional purposes, including a Voice-over-IP service. Being able to create and modify particular records permits you to have different services with different providers if, for illustration, your current host provides stable web hosting, but has issues with the e-mail service, or you simply prefer to get a specific service from a particular company. Although you must be able to 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.