Does it matter whether you use lethal or non-lethal tactics in Deus Ex: Human Revolution?

Solution 1:

1. According to the stealth tutorial video, a lethal takedown makes more noise than a non-lethal one.

2. Neutralizing an enemy without killing will award you a +20 XP bonus ("Merciful Soul").

3. Knocked-out hostiles can be woken by other people who happen to find them. Obviously, this can't happen if they're dead.

I'm not aware of any impact on the story, though there is a Steam achievement (Pacifist) for not killing anyone except bosses.

Solution 2:

you gain more experience when you do a non lethal takedown, the bonus is called Merciful Soul

Merciful Soul: neutralize an enemy using non-lethal methods (20 XP)

There are also other types of xp bonus for every enemy you come across, see this post for more information.

To maximize your experience, you will want to do as many double takedowns (none lethal) as possible and normal none lethal takedowns otherwise.

And killing enemies makes more noise where none lethal takedowns are virtually silent.

Solution 3:

there are some minor differences i noticed if you went non-lethal for the first mission and killed nobody the dialogues change the cops have nicer things to say and Maliks dialogue is also different