There are myriad reasons why owning your domain name (or becoming the registrant) is beneficial to your website and your business. But perhaps the most important reason is control, control over your own property.
A domain name is a piece of property. Whoever registers it, owns it. If you read the terms of service for your Facebook, or Twitter or Yelp or even a blog registered with blogger, you’ll discover that you don’t really own any of those pages or profiles. These can be taken away from you at any time. A domain name gives you a brand name and ownership, and it belongs to you for as long as you want. Owning your own domain name is like living in your own house instead of a rented apartment where your landlord sets the rules about what you can do.
Owning the hosting and files of your website without owning the domain name is almost like living in a rented apartment, you can own everything inside the apartment but the apartment its self is not yours and you can only live in that apartment as long as the landlord lets you. If they ever decide that they want to sell the building to another landlord, or rent it out to another tenant, they are free to do so and you would be forced to move out. In website terms, if the owner of the domain decides to sell the name to someone else, the website you have associated with that domain name will have to be taken down or moved, and if that happens any of the SEO and branding you have built around that domain name will disappear and you would have to start from scratch.
by James Maston