It is the first thing you see and the last you think about. Designing for users from the ground up allows for increased usability and keeps them coming back to your platform. A striking design solidifies their choice.
One size fits all is good for one thing: not fitting anyone in a manner that would suggest the word 'fit' still had any meaning. A focus on critical systems and strengths can lead to market advantages.
Like the minute difference between finesse and fineness, your carefully constructed idea can result in being like an exotic automobile or a sports car with boost. Which direction are you aiming in?