It's only a few degrees, but the difference between -1C, and -4C feels noticeable. It's around the difference of "I'll probably be fine with just some track pants if I keep moving", and "no, I should definitely put on some wool longs underneath".
And it nips my cheeks more.
I probably didn't need to put on my studded shoes for today's walk, but it looked so frosty outside that I did it anyway.