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There's no need to do this, unless it's not stable. I have both enabled on my board and have done since the day it was installed and I run at 3.6ghz with zero issues.
For me, it is well worth keeping it on for the powersaving. Less power = less volts = less heat = less noise needed to cool it when just browsing or doing other basic stuff.
It stops the multiplyer dropping to 6 from 9. It's a prefence I guess, but I prefer my CPU 'on the ball' at 9x all day everyday.