It's easy to spend months working on the perfect product, only to launch and then... nothing happens. We see it happen, literally, all the time. This can be quite frustrating, and can make you waste a lot of your precious time.
You can avoid this and save time by testing your ideas quickly. How? By creating a "fake product" and measuring the results. Confront your product idea to the real world, and see if there's really a market for it!