Originally Posted by
canklecat
Be careful with maximum insertion too. Some headsets narrow a bit toward the bottom, so the wedge can't properly grip the sides when the stem is fully lowered. Had that issue with one of my bikes and couldn't get the handlebar low enough to suit myself. Easiest solution was to swap from the riser bar to flat bar. Problem solved.
Here is a article with a diagram which shows what Canklecat is describing.
https://www.sheldonbrown.com/handsup.html#danger
You will want to tighten the wedge bolt enough that you cannot rotate the stem with moderate pressure, but not so tight that it cannot move at all, so that you are less likely to be injured by the bar in a crash. Do this with brake and shift levers as well, to lessen chances of damage as well as injury.