What good are pajamas (jammies)? They do keep you warm. When you roll over on the sheet, and they stay connected to it? Out pops your boob and the pajama material goes in places that it is not meant to go; on both the upper and lower half of your body. Those are just cardinal sins that are not meant to be.
Jammies have their time and place, like sitting in bed watching TV, or after you come home from a long day. Even on those days off when you just do not feel like getting dressed and sweats is too much of a hassle.
Actually, sleeping in them though? Who has mastered this with any success? Waking up feeling like you have had string strung so tight up your private parts, or across other parts of your anatomy, when you turn over? Only once you have them removed feeling like you have been skinned and leaving a bruise taboot. Who wants this trouble?
I suppose if the heater, a.k.a. the significant other or pet, is not available; nor a lot of blankets then you must do what you have to do. However, being raised in Wyoming and below 0 temperatures at times, pajamas are just not worth it in this case. Long Johns are better if you are short blankets, otherwise turn up the heat or find a heater for sleep. Leave the jammies for the stuff before bed.