Join Chris Nodder for an in-depth discussion in this video What are the uses of scenarios and storyboards?, part of UX Design Techniques: Creating Scenarios and Storyboards.
Scenarios and storyboards provide a reality check for your design, helping you to consider how the interaction will play out in a real environment. Once you've used ideation techniques to create some concepts for how you might want your new interface to behave, it's time to create a story that incorporates that behavior. There are a couple of reasons to do this. One is, that it lets you describe the behavior in more detail to other people. The other reason is that by walking through a user's typical interaction with the interface, you'll end up with a deeper understanding of how well your design idea would work in reality.
If you rush straight from ideation into building a solution, you're likely to miss out on some important nuances that always shows in an interface when parts of it look like they were tacked on later. The truth is, they probably were tacked on because the developers didn't take the time to consider their user's end to end interaction with the feature. That means they had to go back and add things or change the interface in an attempt to make it fit better. Instead, scenarios and storyboards ensure that you can tell a good story about how your proposed idea helps your personas to complete their tasks, and how it removes their pain points, and meets your goals.
Scenarios and storyboards help you get closer to a true design solution. And they provide a great communication tool for keeping the whole team on track as you start development work.