Ever dived into a river without knowing its depth? That doesn't look like a good decision. That's how it looks when you don't prototype your product before launching. Prototyping is testing the depth of the water before diving. You are simply testing the desires and expectations of your user, taking note of their reactions and comments.
Prototyping helps you discover the faults in your design early enough, and early detection can avoid having issues in the final production. You get to see complicated features, features that are not well positioned, or those that are not needed at all.
More so, in the world of digital product development, the mantra "If you build it, they will come" does not apply. As a result, it's always a good idea to test prototypes to guarantee that what you're producing connects with and will be used by your target audience.
Prototyping is also cost-effective. You will save a lot of money if you prototype, test, and iterate on a product early. The risk in launching a product without iterating is that you discover the faults in the product after launching, which will result in you spending more to fix that error, but early prototyping saves you from that hassle.