One clause, and the direction of it is the whole point: attacks that target friendly CRONOS and TALOS units with a Strength greater than that unit's Toughness have -1 to wound rolls.
So it protects your Pain Engines against high-Strength attacks specifically. Lascannons, melta, power fists and monstrous claws all get worse. Massed small-arms fire that was already wounding on 5s or 6s gets nothing worse, because its Strength is not greater than the target's Toughness.
That direction matters because it decides what the detachment is for. A Talos with a minus to wound against heavy weapons is an objective-holder your opponent has to over-commit to shift, and the natural counter is volume rather than quality.
Read the target restriction too: it names CRONOS and TALOS units only. Your Wracks, your Haemonculus and everything else in the army get nothing from the detachment rule. The 2-DP Covenite Coterie applies the same shape of protection to every Haemonculus Covens unit, which is exactly the difference between the two.
The pack states in the rule text itself that this detachment has the COVENS tag and cannot be taken with another COVENS detachment.