Some interactions, such as grabbing an enemy from behind cover, allow you the choice of either killing the enemy or knocking them out, and you can always put a bullet in an unconscious enemy's head. Is there any significance to the decision of letting them live or killing them? Will one option offer better rewards than the other?
You will lose more points if you kill the non-target person as opposed to simply subduing them. As outlined in my answer here, you can gain those points back by not being seen and hiding the body.
If you're wondering about whether or not they will eventually wake up from being knocked out (as in previous Hitman games), I have neither experienced this in-game nor have I seen anyone comment on the fact that they do.