A very useful addition to take into the Backcountry!
For a long time when I went to bed in the woods I would just roll up some pants or fleeces as a pillow. Now I stuff this with things during the hike or climb then at night put some layers in it and sleep way better. It only weighs a bit more than a regular stuff sack, and is worth it's weight in gold. How many times have you made your pillow and woke up in the night to it all undone and ruined your sleep? This fixes that problem well.