Planning out your business on paper first gives you long_term benefits with potential investors, employees, vendors, and suppliers. The business plan becomes your roadmap to success, with pertinent data that shapes the course of your business start_up and lets you adjust your journey as contingencies arise. Business planning templates are readily available and data sources abound at your fingertips. You will achieve a solid understanding of your business as you work through each section of your plan.
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.