I used bag liners for years in rifle season conditions. I have a new 0 degree that keeps me toasty but a bag liner plus a decent bag is nice in some circumstances.
I still have my OG woobie and my "Canadian woobie" that the Army started issuing in 2008 prior to going overseas. It's a zippered woobie with a poncho head hole. My kids always steal it from me. Hands down the best sleeps I've had were in that thing.
Something about curling up in my woobie brings back memories of quiet nighttime OP shifts in Panjwai. The cold mountain wind blowing through as the sun pierces the horizon and the valley starts waking up.