Yes, for me, it is just and extra layer of clothing, but not part of my core clothing system that I use to gauge how "low" of a temperature can I push my sleeping system.
Would never sleep in my wet rain gear, but if I was freezing my butt off and the rain gear was dry, I would definetly put it on as an extra layer of clothing for warmth.
I normally carry a garbage bag in my pack as a multi purpose pack liner or for something to place my wet gear in so that it does not get my other dry gear dirty or wet.
My emergency clothing is my BPL merino wool top and bottoms for next to skin base layer, which I only use when I am in camp, sleeping, or if it is really cold.
BPL Merino Hoody is my base layer/next to skin layer that I hike in.
Monbell Thermawrap Jacket as my insulation layer
Wind shirt as another layer
Rain Gear as my possible last layer for insulation.
My style of hiking would probaly have me hiking all day til it was time to stop of the night and make camp.
If my rain gear is not dry by then, I would stuff it in my plastic garbage bag and set it outside my bivy & tarp with a rock on it to keep it from blowing way. Or, I might have it in the bag at the foot end of my bivy to keep it out of the rain.
Hope this helps.