A valuable source of information about your business that may be required by third parties ; Improved use of your company personal resulting from participation in the business planning process ; Increased employee motivation ; Increased profits and sustained growth.
I teach that you should seek to learn from competitors; obviously never copy another business's idea or what they are doing, but you can absolutely learn from their mistakes or see what they are doing and discover ways to improve it. All of that analysis belongs in your business plan: make sure you have your competitors under the microscope and make sure that is a solid chunk of your plan. That is some of the best research and information you will gather about what will make your business successful in future.
I say that because of course you need to be careful with commercially sensitive ideas, as you do not want to pass your plan on to someone in the pub who then starts your idea before you across the road.
I often see people split into two camps. On one hand those who almost ignore competitors in their business plan, because they do not want to think about the issue yet and feel so confident they have a great idea for the market regardless. But I recommend not being overconfident when it comes to competitors. They are still there for a reason, they are still around and in business for a reason, so view them with that in mind.