I'm of the opinion that really cranking down on compression sacks isn't good for a sleeping bag.  

You can break a soft steel bar by bending it back and forth enough times.  Kevlar fibers get brittle and break after repeated bending.  Aircraft hulls develop stress cracks after repeated expansion/depansion (ha! I made up that word) cycles.  So why does anyone think that supercompressing down isn't bad for the down fibers?

There is a difference between stuffing the bag into the usually almost too small stuff sack you get with the bag, and doing the compress the bag with cinch straps till it squeals overdoing it.  Your bag will last longer and maintain more loft the less you break the down fibers.  How much is too much, and how long it takes before you lose loft is probably direcltly related to how much you crush the bag.

For the most part, I don't see a whole lot of advantage to super compressing a bag - you gain only marginal space, as compared to the normal stuff sack you get with most bags.  IF it made the difference between taking pack A and a bigger heavier pack B, its probably worth doing, but otherwise why bother (I know, I know, its like crushing aluminum beer cans on your forehead - it just feels good)

If you look out on the many backpacking forums, you see a mix of opinions on this - no way is it decied/proven/concensus that compression sacks won't hurt your bag - eventualy

I have 4 Marmot bags, one mOuntainsmith and one Montbell bag that are all in the 800 to 900 fill range - none of them came with compression sacks - wonder why?
the only two bags I have that came with compression sacks were an REI bag and an EMS bag - both of lesser quality and more dubious temp rating.  Unless something has recently changed, you don't see the best quality bags coming with compression stuff sacks - wonder why

One reason for that I think, is that the main reason for buying a quality down bag is to reduce weight  - it is counter to that idea to bring a much heavier compression stuff sack than it is to bring the normal, lightweight sack that is included.  And since I go as ultralight as possible, I use even lighter stuff sacks that save me 3 or 4 ounces or more per bag.  That is a better tradeoff for me - i.e. less weight vs less volume.

edit: - not sure, but I think the original intent of compression stuff sacks was to make it easier to pack your bag - i.e., you were given a much larger size stuff sack so it was easy to put the bag inot it, and then you used the compression straps to pack it down to a more reasonable size.  nothing wrong with than concept if you don't overdo it.