Prototypes let simulate final product before it gets into production. Testing ideas with prototypes gives you confidence and it may save a lot of time when requirements change.
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Making wireframes at first is a good way to start. When all elements are in place adding animations, gestures and transitions become easy and pleasant work.
Test solutions on early stages , it will help you make better decisions and keep your product well thought.
You can almost feel like you are using real app. Test different interactions and experience them right away!
Make development process more effective. Reduce teams communication buzz providing them self explanatory prototypes.