In your opponent's Command phase, roll 2D6 for each Afflicted enemy unit, subtracting 1 from the result if that unit is Below Half-strength. If the result is 6 or less, that enemy unit suffers D3 mortal wounds.
Work through the arithmetic, because it is what makes this detachment different. A 2D6 roll of 6 or less happens about 41 percent of the time, and about 48 percent with the -1 for a unit below half strength. So each Afflicted enemy unit is roughly a coin flip for D3 mortal wounds, every single one of your opponent's Command phases, for free, with no command points and no models committed.
The consequence is that the number of Afflicted units is your damage stat. Three Afflicted units is a bit of chip damage. Seven is a real phase of shooting that costs you nothing. That is why the whole rest of this page is about Contagion Range rather than about Terminators.
The Below Half-strength modifier tells you what kind of damage it is. It gets better against units you have already hurt, so it finishes things rather than opening them, and it interacts well with anything else that punishes a weakened unit.
One more timing detail: it fires in your opponent's Command phase, including the first one. Anything Afflicted on turn one already pays out, which is unusual in a faction whose aura starts at 3 inches.
At 2 DP it leaves 1 DP spare at a 2,000-point game.