Is there a big difference if an automaker doesn't tighten every bolt in the motor, if they don't use quality stitches for their seats, if they don't polish every panel on the automobile?
Is there a big difference if a chef adds a little too much salt, or too little spice to their dish?
Does it matter if the phone is going to be held 50cm away? What if it's not?
As a designer, your goal is make something feel and look absolutely perfect in every imaginable environment. These little details are what separate a good design from a breathtaking experience. These little details are what separate a car like a Honda from a Ferrari. These little details are what separate Dell from Apple. My point is, designers sweat the little details because in the end, those little details can and will build up to make a huge difference in your end product.