There are many added benefits to having a registered mark; here are some of the most powerful ones. Once a mark is registered on the Principal Register, it gives the mark nationwide priority, even though you may only be selling your products in 15 states. In comparison, a common law trademark (simply using the mark) is only effective in the states where it is currently in commerce, so your mark would have to be consistently in use in all 50 states. Most small businesses do not expand throughout the country overnight, so another business has the ability to stake its claim on a mark in a particular territory that you have not yet grown into. Registering a mark with the USPTO gives you priority over geographical areas in the United States where your products have not yet entered.
Once you have used your mark continuously for a period of five years you are eligible to apply for incontestability, which eliminates the most threatening arguments against your mark.
By having a registered mark, you can greatly reduce the number of people that infringe upon your mark, simply because the mark is included in searches performed on the USPTO website. Most business owners would prefer to come up with another name for their business or product to avoid a conflict. Additionally, the USPTO will not register confusingly similar marks.