The need to purchase a domain is due to several reasons, among which there is the most significant one. This is having your own domain for branding. The brand being hosted looks very unprofessional own website at such an address as brandname.wordpress.com. Web resources with their own domain name look more authoritative.
Your own domain name is much more than that. The reason people visit a site is because they have complete control over the site.
When using social networks or creating a resource on free blog providers, as well as when trying to make money on eBay or Amazon, the user is completely dependent on such resources. At changing the conditions of service or the disappearance of any services, the owner of the resource begins to feel problems. If the decision is made to register a domain, you should expect to rely on someone else will no longer be needed. The domain name will belong to only one user who has completed the registration. He will also have control over him and the right to manage.
Managing e-mail addresses that are associated with a domain is the task of which server the site is located on. The owner has ownership or sale rights, that is, with his own domain he can do absolutely whatever he sees fit.
The positions that search engines give out on the resulting pages depend on which domain is used. Older domains are given higher priority positions, which are mainly affected by citation index. This means that search engines determine the influence of the site, which is displayed based on the number and weight of links that redirect to your web resource. But when you own your domain, then the earned links will be given with all their value to another.