It's Comfort vs. Extreme Alpine efficiency, the two opposite ends of the spectrum (Norman Clyde vs. Mark Twight). For fast & light Alpine climbing, yeah - wear all your clothes and cover up with a light bag. I've heard that some extreme climbers wear a down parka and just slip their legs into a half-length bag. It makes sense if you're doing a fast-n-light 24 to 48 hour out & back & you really only need about 40 winks on a bivy ledge. But if you're doing a longer climb with a more liesurely approach and you really want to get some rest the night before summit day, wear only a base layer (or less) and get in a big, puffy warm bag. Yes layers of clothing do provide insulation but stacked layers restrict circulation and aren't all that comfortable. What works for you? maybe one or the other or something in between.
Even in the summer, I bring the lightest bag possible and sleep in whatever the appropriate amount of clothes to keep warm. For nearly ever trip in CA I take my 32 degree bag (relatively new and lighter than the 40 deg bag that used to be my standard). I can use it almost year round by sleeping in all my clothes. Sometimes in winter I need to take my 20 deg bag.
Not much point to carrying all those layers along if you are going to pile them up in the tent next to you at night. Spoon your partner if you need something like that next to you![/quote] The same could be true for those who climb hot but sleep cold, it's purely trial and error for most who have climbed for many years