I've never used it, never felt I need ANOTHER product in my shaving routine. I use pre-shave, soap, alum if needed, aftershave and/or a balm. I'm cool with that. No need to add witch hazel.
I have read that the tannines dry out the skin, which in turn causes rash or acne. Not something I'm willing to pay for.
If you are using alum, you might not need witch hazel. However, I do not know where you are getting your information that witch hazel dries out the skin more than alum.
Witch hazel does contain tannins, but for those with acne, that can be a good thing as it acts as a anti-inflamitory and astringent that is useful in minimizing acne breakouts. Thayer's makes an blemish clearing acne cleansing pad that combines salicyclic acid, aloe vera, and witch hazel. You might want to do further research.