I carry the Heetsheets version (3.5 oz), which I use as a backpack liner and ground cloth. It's also useful to cover up the bottom half of my sleeping bag to keep off the rain. I can thus huddle down to the bottom of my tarp or tarptent to keep the rain off my head and upper torso. (I've never used it to cover the whole bag so that too much internal moisture will not accumulate.)
Oh, yes, and I can also use it inside my bag if my sleeping bag is inadequate to keep me warm.
It's tough as nails, so it can stand quite a bit of abuse even from repeated uses.
BTW, I just fold it up and put it in the knapsack when I'm not using it as a bag liner.
I've pretty much eliminated stuff sacks that way -- including the one that formerly held my shelter. Small stuff like medical supplies (what few I have of them) and personal items all go in the same cuben-fiber sack.