It makes the difference if it's the "compressing" itself, then taking it out of the suff sack only to stuff them back the next time to use it is actually adding one additional compression cycle than otherwise the bag goes through. It might actually shortens the life of the bag rather than extending it.Compressing/compressed... tense doesn't matter if it breaks the feathers no matter what.
Not to sidetrack too far away from the topic. For the longest time, backpackers fold their tent meticulously each time after use. Only to find it often tears along the folding line! So nowadays, the recommendation is not to fold them into tidy pile but just randomly stuff them back into the bag so there's no reenforcing a fold line!
Like I said, there could very well good reason to follow the manufacturer's recommendation. Just that particular explanation doesn't seem to make sense to me.I get my info from the manufacturers and pass it on.