[RERomine]

In general, low visibility favors the attacker in assaults and advances. The numerical advantage the attacker has can be reduced as they approach with artillery and long range direct fire, but not if you can't see them until they are only 300m away. At least against the AI, you can be sure it won't attack on a narrow front and just try to punch a hole in your line. Instead, it uses a broad attack meaning you won't have problems finding something to shoot at. The down side is you have to pretty much watch everywhere, even of you don't protect everywhere.

There are two exceptions to low visibility favoring the attacker. One is air support. The attacker has more points to spend so could get more air support than the defender, if it was available. The other is if the defender has weak AT guns. In low visibility situations, the attacker will encounter such guns at close range where they will be more effective. That is easily countered however by proper recon.