The one present before TTK was released. NF completion gave the player a week long boost in all activities involving leveling gear. It was like the weapon telemetry but was universally applied to all gear until the next reset. It stacked with telemetry. That buff.

Sorry mate. Buff was withdrawn when TTK dropped :(

I am aware of that. I also withdrew my NF activity for that reason. I only did NF for the guaranteed buff. Rewards had little meaning to me for I had every weapon and armor piece the game offered in legendary and exotic variety. Now, the buff is gone I see no reason to suffer the NF bullet sponges for junk. I did it this week to see if Bungie was serious about its 'improved reward' talk. The reward, a 300 light legendary, confirmed to me that I can waste time and ammo elsewhere in the game. Good luck to those of you still doing night falls. Heavy ammo is too expensive for me to waste it that way...