So when the gyro stabilised HSI fails how are you going to turn onto a heading using the compass?
Std IFR procedure is to fly a rate-1 turn and time it.
So note your heading (when straight and level); figure out how many degrees you want to turn. Then start stopwatch and start turning at rate-1.
This works a LOT better than trying to figure out a heading from a magnetic compass, and is the only procedure I teach IFR students.
That said, its always good to have the knowledge as to why you should not rely on the magnetic compass during turns/acc..