Each domain name that is registered and hosted has a great deal of DNS records - some of them are created automatically when you host a domain, others can be set up manually if required. For example, the A record of a domain name is its IP address i.e. this record shows where the site is located; the MX records show where the emails are managed, while using an SRV record you can use a domain address for unconventional purposes, for instance a Voice-over-IP service. Being able to set up and modify particular records enables you to have different services with different companies if, for illustration, your present host provides dependable web hosting, but has difficulties with the email service, or you simply prefer to get a certain service from a specific company. Even though you can create and modify these records freely and with no restrictions as you own a given domain, a lot of companies charge extra to give you this option.