Take it when you want to play the mission aggressively with any Chaos collection. The army-wide Assault is a genuine quality-of-life upgrade for a faction full of Rapid Fire bolters, and +1 armour penetration against objective-holders is a buff you will use every single turn without setting anything up.
Be clear-eyed about the price. At 3 DP it fills your whole 2,000-point budget. Its rule is also the least explosive of the four 3-DP options: it is a flat, reliable improvement rather than a combo engine, so it wins by consistency rather than by spikes. And two of the four enhancements only pay off when the bearer is wholly within 12 inches of your opponent's deployment zone, which is a real risk to take with a character.
Sample gameplan: put Mark of the Hound on a character leading Legionaries or Chosen so they start up the board. Advance everything under Assault and shoot anyway. Spend Warpcharged Engines to put a Rhino where it should not be, disembark, and use Ruinous Raid on the objective fight. Hold Unfailingly Obdurate for the return fire, and use Opportunistic Raiders at the end of the Fight phase to leave a melee you have already won and take the next marker.