e.s. kohen wrote an answer about Gregory Denali Pro 105 Backpack - 6100-7000cu in on June 24, 2011
Many moons ago, people disliked their sleepbags smacking them in the thighs, and these quick access pouches were created for that.
This, in my opinion, is a horrible use. I never get my bag out first. I always go for my tent. I have a Marmot Thor 3P tent that I store in the bottom, and put my stakes down the "sides" of that pouch up the walls of the bag. It is completely accessible for in this way. Once i get my bag in my vestibule, then I open it from the side zip pouch and start gutting it.
I also like to keep a low to mid center of gravity on my bag to avoid losing balance. (Totally recommend trekking poles when you have a high center of balance).