Trademark registration is required if someone or a company wants to be protected by the exclusive bundle of rights granted to a registered trademark owner. Trademarks are considered to be owned once they are publicly used in commerce. It is against the law to intentionally copy a trademark belonging to someone else even if it is not registered.
If someone unknowingly has a similar trademark as another, the first one to get the trademark registered with the United States Patents and Trademark Office will be the official owner of that trademark regardless of who was using it first. Once a trademark is registered with the USPTO office, it is protected and cannot be copied in. The good and services provided also cannot be used by a company sporting a similar trademark to avoid confusion among consumers.