[Suhiir]

I'll second that.
Picklists are not something the average, and most above average, players even want to consider messing with.

As DRG/Don said they select formations specified in them as "common" (around 75%), "uncommon" (around 20%), and "rare" (around 5%) during a given time period.
Unless it's a very low points battle they will (almost) always select some sort of mortar and anti-air formation after selecting the first (usually) infantry formation (with any inherent mortars and AA it may have). Then based on what the picklist designer knows/believes to be the typical (i.e. foot vs motorized vs mechanized vs armor) types of formations used by the nation it will go thru and select formations till it runs out of points to spend.
Typically every 3rd or so formation selected will be mortars or AA weapons, thus the AI tends to field a lot of both.