For wild birds brining opens up vast cooking options that otherwise would produce dry, tough meat.
It’s also excellent for domestic poultry and pork, but only those that have not already been “enhanced” by injection with salt water – as most are. Read the label.
Like many other brine recipes, this includes sugar. The primary impact is to improve surface browning (Maillard reaction) when cooked. It does not tend to sweeten the food.