To begin with, the car just looks better. Sad to say, we live in a world of people who make snap judgments about others based on a one or two second first impression. If that impression is you getting out of a filthy car to go into the store, the person next to you may assume that your personal habits and housekeeping are no better.
They will perhaps feel “creeped-out,” and be careful not to come to near you, for fear of catching fleas, cockroaches, bedbugs or that general-purpose ailment from your childhood, the dreaded “cooties.”
As you clean your car’s exterior is a perfect time to check for things that may be working loose such as license plates/frames; headlight and taillight lenses; mirrors; valve stem caps; hub caps and antennas.
It pays to use the time down on the ground while cleaning the wheels to take a peek underneath the chassis to be sure you have no loose or broken cables or hoses. A worn or broken brake fluid line, for example, is not something you want to find out about while driving.
While washing the car, pop the hood and take a look inside the engine compartment. Look for loose wires; broken cable ties; you don’t want a wire hanging and getting snarled in the fan; loose connections on the battery; loose connections on the air cleaner cover, and so forth. Check to be sure there is no corrosion built up on the battery connections as well.