The main advantages, to me, are lack of stretch and creep, and increased durability. It can vary depending on the material, and how many strands you use in the string.
There's no huge performance or noise increase (if you compare apples to apples). Proper tuning and silencer placement is, in my experience, where you will make a difference with noise. How the string is made (regardless of material) can also make a difference in noise.
Short answer: longer lasting string that doesn't vary in brace height nearly as much.
Chad