Play in the quick release and the '3rd hole'

So ive noticed a slight click in my wheel (GT-21 with SC2pro) after straightening the wheel following sustained high load corners like 130r at Suzuka. I concluded it wash something in the wheel/hub and after taking everything apart and tightening it I found that doing the 2 scews that tighten the pin on the QR has done the trick. I did them up to max tightness and didn’t back them off a turn as per the instructions (I don’t change wheels so not fussed about removing the pin very often)

Now, I noticed there is a threaded hole in between the 2 tightening screws on the motor side QR. What is this for? it looks like it will engage the cross pin if a screw hit it. Has anyone put a screw in there for ‘extra tightness’?

It’s for a second pin, or for attaching a security lock/bolt while beeing at expositions or similar. The hole is threaded, so a simple screw with the correct length will do the job. But IMO it’s absolutely not needed.