The fast idle button just opens the throttle as if you were twisting the throttle a-little yourself.
Avoid using it.
If you need to give it extra throttle for a moment in cold weather to prevent stalling, do it manually. Running a superbike at the higher fast-idle RPM is a very bad idea because measurements have shown that it takes as long as 90 seconds for oil to reach the vertical cylinder rocker arms and camshafts. So you're running on a surface film of oil that's left over from your last run until the sump oil reaches the cams. So it's best to wait for this to happen at as low an engine speed as possible.