Every domain name which is registered and hosted has a lot of DNS records - some of them are set up automatically when you host a domain, others can be created by hand if required. As an illustration, the A record of a domain address is its IP address i.e. this record shows where the website is located; the MX records reveal where the emails are managed, while using an SRV record you can use a domain address for unconventional purposes, including a Voice-over-IP service. Being able to set up and modify certain records permits you to have different services with different companies if, for instance, your current host provides stable web hosting, but has troubles with the email service, or you simply prefer to get a particular service from a certain company. Even though you should 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.