That would seem sensible in a civilian bag. A military bag would usually place a higher priority on being able to get out of the bag for emergencies though.
They not only line up but you's be taught to only zip one of them (for the reason stated above)
short and sweet,
If the zips do not line up and one sleeping is open it would keep you warmer the offsetting of the zip ? ......
Yeah it would IF one were left "open." However when I said you're taught to only zip one of the zippers I should have explained the sustem better. When you stuff the inner bag into the outer one, you also snap them together down the length of the zippers. Zipping just 1 zipper closes both bags. Likewise when you stuff them into the bivy bag; the one zipper closes all 3.