Wellll, because it's synthetic (as opposed to down) it's good for damp climes, but it's pretty thick and toasty. However, being a vest, it's not as toasty as a jacket.
How/when I wear my current version: Fall/winter steelhead fishing over a wool turtleneck and Cloudveil bunting top when temps are approaching freezing and I'm standing in 46F water up to my hips. Then it's easy to throw on a windproof anorak and not constrict my arm movement too much.
I don't think I ever wear it except in true winter weather as I'd rather put on a few longsleeve layers first so my arms are better insulated before adding a sleeveless layer. But that's my preference. I wouldn't wear it in what I call "cool" weather (guesstimated air temps of 40-55F).
Does that help at all?
Frends know gud humors when dey is hear it. ~ Da Crockydiles of ZZE.