The bumps on the "F" and "J" keys are there so you can put your index fingers in the proper typing position without looking down. Because when you're typing an amazing Tweet about what you ate for lunch, you need to put as much focus on looking at the screen as possible.
The small hole on airplane windows is there to equalize pressure between the window pains, keeping it from shattering. And pretty soon, most airlines will probably start charging a "small window hole to prevent them from shattering all over you" fee.
The arrow here lets you know which side of the car the tank is on, in case it's a car you haven't driven before. Now that you know this, it will be easier to fill the tank the next time you steal a car.
These holes in the sides of some shoes allow for extra ventilation, keeping your feet from getting too sweaty. Which means these holes make it much more difficult to bug everyone in your house with your gross, smelly feet.
The flap of a toilet seat cover is supposed to go in the bowl. This allows the water to pull the entire cover into the bowl when you flush. Or you can refrain from using the disposable toilet seat cover, but only if you're really into gambling.
The extra pieces of fabric that come with jeans are there so you can test the material in a washing machine and dryer to make sure it won't negatively affect the whole garment. Which is nice, but shouldn't they conduct those tests themselves? Why are they even paying money to Inspector 12?