StackSizeMultiplier is pretty obvious. In increases the size that items stack in as a multiplyer. Ie. normal stack size = 100 and StackSizeMultiplier=5.000000 and the stack size is 500
StackWeightMultiplier is a bit confusing. It actually increases the players carry weight and has nothing at all to do with stack sizes. Exampel. Normal max carry weight 100.0, setting StackWeightMultiplier=2.000 and max carry weight is 200.0, but only applies to players, not tamed animals.
ItemWeightScale adjusts items weight as a multiplyer. Example Normal item weight 5.0, with ItemWeightScale=0.25000 that item will weight 1.25
Then there is one that has to do with game difficulty.
MaxDifficultyOffset works like OverrideOfficialDifficulty on ARK in that it is a multiplyer on top of DifficultyOffset. Dark and Light does not seem to accept anything higher than 1.00000 for DifficultyOffset. Example. Setting MaxDifficultyOffset=5.0000 and DifficultyOffset=1.0 will spawn dinos beteween level 5 and 150.