Doing so will also help you build (and keep you accountable to) attainable financial and product milestones.
Outside of these immediate returns, writing a business plan is a useful exercise in that it forces you to research the market, which prompts you to forge your unique value proposition and identify ways to beat the competition. Doing so will also help you build (and keep you accountable to) attainable financial and product milestones. And down the line, it will serve as a welcome guide as hurdles inevitably arise.