Fiddleback, I agree with your point, and have learned through poor decisions that there are times when I can leave the bag at home successfully, and times where that just means I'll be waking up every hour for some calisthenics and shivering.

The idea that one must carry a sleeping bag comes from habit, people always consider it a necessity. And usually, it is. But with good layering, and a hardy, hot dinner, I've slept plenty of nights without one. Usually that means I wear most of my gear to bed (often including unlaced boots), and sometimes it can involve my hotpad/bandanna wrapped around my face.