Safe to Hit Low
I have come across some people who like to hit but low during Chī Sáu 黐手 and they do this because they cannot hit your face or chest. This is not good since your opponent can sometimes hit your face at the same time as you hit low. So you not hit low unless you are in control of the situation and are covering your opponent’s hands so that they cannot hit you. In this situation you can hit low. When it is not safe to do not hit. Sometimes hitting can become a habit and so you will automatically do it even when your opponent can hit your face.
In particular I have met many big and tall people who hit low all the time but this means they need to bend over in order to hit and so their face is also lower and so you can hit them more easily.
Hitting low when you are in your opponent’s side is better, for example when you opponent punches towards you, you can step to the side and cover their elbow with your Wuh Sáu 護手 and use Dāi Jéung 底掌 to hit them low on the side. Another way is to attack their face so that they block your hands, then their hands are in high position and then you can hit low since you are controlling their hands. But in normal situations you should not hit low.