I agree with Terry on this subject, but I also think it is possible for a car to lose power with parts that help to lower backpressure. For example if a car was making x amount of horsepower and you were to put an offroad y-pipe that caused it to run lean power will probably drop. In my case my car increased power with the offroad y-pipe but then lost power when I put the Pro-M on. If I had put the Pro-M on first I guess I could say it was the lower back pressure of the y-pipe that caused a loss of power. I think it is a good idea to dyno your car as you make changes but you still have to look at the big picture and realize how one part relates to another.
