What do service A and B include on a Mercedes Benz E320 2003 model?

they do these kinda services to check out if there is something wrong in a car or something need to be replaced , I personally don't advice any one to waist his money and his time to do that service , most of the mechanics tells you that the service takes 3 to 4 hours... it costs a minimum of 400 $ and without even fixing any thing in the car.
as long as your car is running fine then you don"t need to waist your money doing these kinda stupid services ,,,