The best thing about vests is they can be worn almost year round, and can be integrated into outfits depending on how much or how little warmth you need. It's easy just to throw on a vest over a button-up shirt and call it a day, but you can also get advanced with this sleeveless garment.
Depending on what the vest is made of, it can be layered under virtually any other piece of outerwear. Vests made of denim, fleece, or are quilted can be easily worn with almost every type of outerwear, and you'll be set for whatever the thermometers read. But if you want to keep it simple and rock a vest and a hoodie, go for it.