If you want to stay warm, wouldn't you want to reduce loss of heat by air moving in and out through the armpit holes? Vests are designed to be worn with/under

If you want to stay warm, wouldn't you want to reduce loss of heat by air moving in and out through the armpit holes? Vests are designed to be worn with/under some sort of outer jacket to provide an extra layer of insulation, without adding an extra 'layer' of sleeves that will just be too bulky or hinder mobility. Another useful aspect is that they pack up a lot smaller and are thus easier to shove into the bottom of bag when you're not wearing them.