As you know, you performed the mesh tuning each time you added new polygons. Why this topic is in individual chapter? The answer is: "Because it's mesh reducing topic".
       The aim of this topic is to get rid of unnecessary polygons.
       Select ALL faces in the object and choose in Objects float bar: Faces > Properties...(or simply hit CTRL-A). In the Attributes dialog box look at the Faces filed that shows amount of selected polygons:

       451 per cars' half is 902 for the whole body. Plus 4 wheels 100 polygons each. Totally the car is average 1300 polygons. It's might be called "we kept the track of polycount", but there are polygons to reduce in this cars' half and it can be reduced down to 400 polygons or less.

       Well, the car is ready to be textured.