Well in theory, as the airstream (or relative wind) runs over your car's body, the smoother it leaves, the less drag you will have.
Ever notice how the rear of your car has huge build up of dust and debris on the tail of your horseless carrage. That is where all the air your car displaces meets in a turbulant collision. Thats a vacuum, which actually slows the car down. So in essence, the add on deck spoilers and lips where supposedly to clean airflow up by evening up the flow, moving the point of turbulance farther back from the car, weakening the effect of vacuum. Wings usually are placed up high in clean airflow and are shaped like upsidedown wings. These are for downforce. There are cars (e.g. the racing Mercedes CLK-GTR) that have bodies that are designed to channel enough air over lips, wings, fences and past dams to creat huge amounts of downforce.
They take a car that has a body shape similar to ours and the make flaps and boundry fences everywhere to reverse lift.
One little tail is gonna do shit for us.
The stuff on the back of my camry and your solara?
Designed to seperate the consumer from currency.
But it looks hot..
When I was buying a Civic back in the 90s, salesman said the rear wing was $600 option as they had to retune the suspension. I was about to bop him when I thought about it, his tech salesman told him that but not the part about trunk lid springs to compensate for the added weight. That was the tuned suspension - the goddamn springs and bars in the trunk. Punk.