I logged the class/effectiveness = total demand values of chaos marines once with their standard (dowpro) rating of 4, once with rating = -1000.
Result : rating is a weight factor only affecting class, not effectiveness. With rating 4 the marines did get a class value like this early in the game
AI1000 00:18 chaos_marine_squad D: 0100 C: 0092 E: 0008
D: Demand = C: Class + E: Effectiveness
As we all know class is the value awarded for having an armour class the enemy is weak against. Effectiveness is the value of our weapon against enemy major armour class.
With rating = -1000 we get this
AI1000 00:18 chaos_marine_squad D: 0008 C: 0000 E: 0008
Class value stays 0 the whole game.
Conclusion : Rating is a weight factor only applied to units armour class.
This has no big impact on future coding but is interesting to know nevertheless.