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.