While air resistance can be a nuisance for a car trying to get higher gas mileage, there are also a number of cases where air resistance is desirable.
For example, air resistance is the reason that a parachute brings a person safely and slowly to the ground
The resistance of the air allows planes to fly.
If there was no air resistance all objects would fall to the ground at the same rate - so if you dropped a piece of paper and a rock from the same height, they would hit the ground at the same time.
For objects that were falling through the air, there would be no terminal velocity - the objects would keep accelerating until they hit the ground.