How do you turn this on? I have the right card for it but I can't find the option to actually turn it on ... or is it just on by default?

Thanks.

Advanced options in the launcher.

Thanks. I know I looked there but I'll check again.

Don't turn it on , why ? I'm on gtx 780ti x 2 sli and you loose instant 11 fps drop around 11% gpu ussage soon as u shoot at ground

I was wondering how it would affect that. Honestly from some vids I've seen it's a little over the top anyway. I just wanted to see what kind of mess I could make, and then probably turn it off again.

Yeah its fun to mess around with but u was at 87 fps then instant drop to 71 fps soon as u shoot once , if your sli it's gpu #1 that takes the hit I Tryed dedicating a 780ti to physx in nvp but doesn't change.... I leave it off. Ya shoot 1000 rounds then throw a grenade in it

Some more infos:

http://www.geforce.com/whats-new/articles/fallout-4-patch-1-3-adds-nvidia-hbao-and-flex-powered-weapon-debris

I'm using the debris effects maxed out on a GTX980, and I'm not seeing any significant impact on FPS. Of course, I'm using V-sync on a 60Hz monitor, so I could be losing some frames above 60 without knowing.