I normally carry a fleece or a down jacket for 3 season backpacking (3 Season for me is high teens or warmer). Occasionally I’ve carried both due to a negative forecast about possible snow, but never needed both (usually just use the down jacket), even with some snow (<1 ft where I’m camped). I’m pretty warmed blooded so never hike in a down jacket or fleece, except maybe the 1st 10 minutes out of camp before I fully warm up (not required, just preferred).
I find my baselayer, long sleeve hiking shirt, sub 2oz wind jacket, lightweight rain jacket (OR Helium II), MLD rain mitts, along with my lightweight balaclava give me all the warmth I’ve ever needed, even with a wind chill hitting me with low 20’s temperatures when moving. At rest, if required, I’m under my shelter so the down jacket doesn’t get wet, though I usually put the wind jacket over it.
