The biggest upside of choosing down (instead of synthetic insulation) is the insulation power it provides. It’s the best natural insulator you can find. Compared to all other alternatives, it gives you the best warmth while keeping the weight low. This goes a long way in terms of comfort and convenience.
Wearing a lightweight vest that feels cozy and warm feels great. In addition, down is known to be very compressible, meaning that you can pack it very tight. This allows you to always have it on your hiking checklist and take it with you because it doesn’t require much space.
Down is the best choice you can make for very cold and dry conditions. It’s low bulk and low weight, while performing great as an insulator. However, it does have some limitations. When it gets wet, it loses all of its insulating properties and becomes really cold really fast. Keep this in mind and have something over it if you expect rainy weather.