Bikewolf

Winter layering system, commuting ...
Whether you need one or not. Anyone that uses / may choose to add a full-zip sleeveless garment, if only temporary? (Or, if not full-zip: a sleeveless shirt?)

E.g. as an outer layer at the beginning of your ride (cold start), or as an inner layer underneath your shell.
Focus on a gilet type of thing, something not too heavy. — However, maybe someone out there that temporary uses a body warmer that gets nicely re-used in a cold office / cooling down fase. I dunno.

"Winter" being early or deep winter to you.

MinnMan

My experience is that my core is seldom cold and I focus on insulating my extremities.
Consequently, for me a sleeveless winter garment would be useless.
Others may feel differently.

ThermionicScott 

I never, ever wear sleeveless stuff, especially in winter. People might mistake me for a triathlete!

epnnf

IDK if its a gilet, but I have a sleeveless vest- the front is windproof; back is mesh. I sometimes wear it above base layer, below outside layer.

wolfchild

I like using vests for certain weather conditions not only for cycling but for other outdoor activities as well...I have different types of vests, some are windproof all around front and rear and others are insulating vests which I use as part of my cold weather layering system. I find vests to be perfect for regulating body temperature, keeping warm and preventing sweating too much under certain conditions and activities.... Just experiment and see what works for you.

rumrunn6

for the most part, I don't see this as an important winter garment for cycling, unless I guess if you're in Southern CA?
there are some occasions, where I've worn a wind breaker vest on a winter ride. but a lot depends on everything else you've got layered on. I like the vest for visibility too
for example, I've got a North Face fleece jacket that gets a lot of cycling use. it's warm, resistant to light precipitation & easy to vent. but sometimes I want just a little bit more chest protection from the cold, until I warmup & since I'm often all in black, it's nice to a bright color for visibility
for me it's a thin cycling jacket w/ zip off sleeves. gotta be one of the most versatile garments I bought. must be 15 yrs old. hardly ever use the sleeves anymore

Garthr

Full zip vests all day every day ! For riding I have mesh back vests of various types and fittings that I wear both over and under other jackets. For example right now with temps in the 28 plus degree range I wear a Craft Extreme LS base layer shirt, a Sportful Fiandre Light vest(or short sleeve full zip), on top of a Fiandre Warm outer fleece lined vented wind stopping jacket. All with Fiandre NoRain thermal bib shorts and leg warmers. The tops are all very form fitting, which is new to me this year as I had always worn loose fitting upper layers before. This works so much better though, more than I ever thought it would or could. While the jacket is windproof, that doesn't mean it's not immune to heat loss. Rather than donning a warmer base layer, adding the wind vest underneath helps to preserve body heat. This works better than simply more insulation as then one can overheat too easy then to cool off you have to expose yourself directly to cold air. That just doesn't work for me, to much of yo-yo effect. With this I can open the front or side zips for heat release yet still have a lighter wind blocking layer over my torso. This works to well in the cold. too slightly cool off without exposing skin rather than a rush of air on the skin which cools too much. Like yesterday I rode 2-1/2 hours in 32-39 degrees with a cold dry heat sucking easterly wind and through all the direction changes with and against the wind, I was steady freddy as far as my core went and I felt terrific when done. In the past with loose fitting flappy upper layers a day like that would been h-e-double toothpicks.