Killing an enemy increases health regeneration for you and nearby friends for a few seconds.
Regenerates +(1...5)% health per second
As with other skills described to last "a few seconds", Stat lasts 7 seconds. Thus, 5 points in Stat will regenerate 35% of your maximum health if allowed to run its full duration.
If there are only two or three weak enemies remaining while you (or some of your nearby allies) have less than half health remaining, it is sometimes beneficial to take cover and wait for Stat to run its full course before killing the final enemy to maximize the healing Stat provides before moving on to the next encounter.