How is this useful in practice? Like this: if ever I get an idea for a feature that seems cool, but would greatly increase video export times, I’ll toss the idea because my goal is to be fast. If I ever find myself adding a lot of complexity to the interface, I’ll have to take a step back and ask myself, “Does this slow people down? Does it make the app less intuitive? How does this affect the user’s workflow?” Another example: I’m planning to make Snapthread a universal app. I’ll probably do a lot with drag and drop, because dragging and dropping things on an iPad is both fast and intuitive.
Source: Staying Focused with an App Mission Statement | Becky Hansmeyer