FWIW, I had never put mine in the bag until I gave up on using it almost a year later- and then just to keep it from getting contaminated. Beforehand, it was 'stored' in newsprint that was replaced when it became saturated, and that was often.
I didn't feel comfortable putting any pressure whatsoever on it. Basically, I just used the tips. Even so, at the end, I was still getting some streaks, and the sides and rear of the car really accumulate more dust than I am comfortable taking off with it.
Another duster, another car, another color, another garage, other usage, other roads... anything will change the equation.
I agree that most people never wash them, although I have no idea what the implications may or may not be.
I just basically resigned myself to letting the thing get dusty and washing it when I couldn't stand it any longer. That's a bit disappointing, because the thing retains water in millions of places.
I've had good luck on the tires and interior, however.