For a mark that is not registered, you may rely on your rights under the common law action of "passing off" to protect your mark against imitation or infringement.
However, if you register a trade mark in relation to your goods and/or services, you are effectively gaining a statutory monopoly of your mark. A trade mark can add value to your business because it can be used to protect your market share, you can license it to third parties such as a franchisee, or you can sell it outright for a specified value. You can also use a trade mark to help you to raise equity for the development of your business.