Sadly all of these things can leave the finish of a car looking less than perfect and at worst, dull, faded and covered in light scratches, swirls and other marring. Not only does this detract from your car's appearance but it ultimately reduces its value as well.
For the vast majority of cars, paint correction really can make a substantial difference and will completely remove or significantly reduce most marks. Not only this, but the resulting finish will have an amazing gloss, depth of reflection and slickness.