To me, your eliminating the last defense against misread weather forecasts or surprise wind/rain events than make it seem much colder than it is. If you're tired from the trail, you're body will have a great more difficulty maintaining core temps in the wee hours. I was much more discomfort tolerant when I was younger, so my choice now is to almost guaranty comfort and safety as much as I can. A sleeping bag/quilt is part of achieving that; sleeping in my jacket was something I did at the base of climbs or on quick trips when I was young. If you think you can have a weight and financial savings by sleeping in your jacket, try it at home first and see how it goes.