Pretty much what it says on the tin. Any pawn with a ranged weapon whose target closes to melee will retaliate with punching instead of firing at them. For example if you have a pawn set to respond with attack when it is aggressed by, say, a hungry timber wolf, outside of being drafted, it will never use its ranged weapon once the wolf gets into melee range. Which of course leads to immediate death of said pawn, barring intervention to draft them and force them to fire, but they've always already taken at least some unnecesary damage with a lot less than they could have dealt back out.