When it's really really cold, yes. But when it's cool through prettydamncold, a vest keeps me warm and affords excellent range of movement. I wear a puffy vest for cool-weather dog walking until I absolutely have to put on a coat.

[Disclaimer: I am insanely allergic to down so my puffies are synthetic. I breathlessly await the announced-but-not-yet-available Smartwool-stuffed puffies.]

Layering and when working you may want your arms unencumbered but still want to keep your core warm. or what workerant said.

warm vests are good for when you're hiking in cold weather. Or when you want a warm core with e.g. a waterproof shell over top.

^^^^^What everyone else said. With a sweater, I love my down vest. I've also worn it under my rain slicker when I needed something waterproof but it wasn't as warm as I needed.

I would sometimes wear mine around the house. Kept me nice and cozy.

A vest keeps your core warm and warms your blood before it goes out to your arms and legs. They are almost a necessity if you work construction.

I find a vest to be an indispensable New England layering element. It keeps your torso from getting that cutting/chilling wind effect, but lets you move around without feeling all "I can't put my arms down!" It's amazing how warm you can be in a vest, a good wool hat, a scarf and a pair of gloves.

And because the temperature changes a lot in a day, it's kind of ideal to do things like that. So here's the scenario: it's Saturday and you're going to go, like, hiking and apple picking and then have lunch in a pub somewhere. When you get up nice and early to get going, it's butt cold, like maybe 20. You put on your vest, gloves, hat, and scarf over your regular clothes - like a warm shirt and jeans - and if it's really cold, maybe you have thermals under the warm shirt and jeans. You head out. At first you're all cold. But then as you hike, you get warmer from moving around. Also, the sun breaks the horizon and the temperature starts to rise. It's 30, now it's 35, now it's 40 and you're all flushed and sweaty. During this temperature climb, you might first take off your scarf and throw it in your backpack, then your hat, then maybe unbutton the vest, then take off your gloves. If you get really warm you can doff the vest too, and even unbutton your overshirt and just have your thermals peeking out there. Roll up your sleeves. Jam all your accessories in your bag. During the indoors part of your day that's all you need.

As it gets cooler you do the whole thing in reverse. Sun starts getting low, and first you button back up, then add in your hat and gloves again, and finally the scarf if you really want to maximize the warmth. Sun is getting low by 3 PM and temperature is diving.

It's really good to be able to adapt like this with small, light pieces. A vest is still way lighter and less bulky than a down coat or any other kind of coat, and it just seems that your choices with a down coat - on or off - are limited. You get too hot, coat comes off and now you have to lug this bulky thing around and eventually get cold again. Whereas with a vest, you can keep yourself reasonably cool by opening it up and taking off the gloves and stuff, letting your arms work like heat transference thingies by evaporating excess heat into the air even while you still wear the vest.

It also frees your arms to do stuff that would be too clumsy in a bulky coat. E.g. (as ardiril said) construction.

Wow. I had no idea they could be so versatile & useful! Makes sense that you'd still have full range of motion but keeping the heat where you need it. Thanks, guys. :)