Many years back I asked the Yamaha reps at Bike Week in Daytona what that was for and they told it was a deflector to fuel that could get spilled, it supposed to keep the raw fuel off the hot engine parts.
It is supposed to be on the left side, One of the bikes on display that year someone had put it on the right ride, when I pointed that out to them they got all red faced and took the bike off display to fix it, the next day it was back with the deflector on the correct side.
I also know that the wire part of that is there to keep you from putting your leg on the valve cover, because if you wearing shorts and your leg touches that wire, you pull back before you can close to the valve cover, it gets plenty hot.