A rough concept or business plan can show how and with what resources you intend to realize your idea. It also forces you to thoroughly think through your idea and helps you determine how realistic it is. If you know your strengths and weaknesses you can decide whether and how to proceed.
A business plan defines your strategy, the type of business, financing, market, projected turn-over, competitors, marketing and intellectual protection strategy.

A business plan is often essential if you want to sell your idea or find a partner for the production or marketing of your product.