I hate the bulky feeling you get when pairing layers under a big winter coat so the trick is (for warmer winter days) layer under a lighter weight winter coat. (pearlsandtwirls.net)
They allow flexibility to wear alone on warmer winter days as well. (heatherlingerfelt.com)
Today, for instance, it was a rather warm winter day but gloomy and raining. (theinspiredroom.net)