What are the pros & cons of this method?
Pros
Anyone can sketch ideas, which makes paper prototyping an inexpensive way to get the whole project team involved. You can make a paper prototype in just a few minutes, which makes them great for generating a large amount of ideas quickly. The freedom of pencil and paper facilitates experimentation and new ideas.
For some people, stripping out colours and imagery allows us to create a distraction-free design – ensuring we are getting focused feedback on fundamental functionality.
Cons
It doesn’t matter how crafty you are with a pen, a paper iPhone with ink marks on it is unrealistic and will make a user feel disconnected from the experience - using an actual device with functional buttons is more believable.
They rely a lot on the user’s imagination, so what the users are thinking may be different than what you originally intended, therefore the user’s feedback might not reflect this.