It has to do with how the engine recommends you equip certain items when you are moving them around the inventory. The VALUE column is multiplied with the stat's real value, and the resulting number is added to a total "rating" count. The higher the rating, the better the item in the eyes of the engine.
Any stat not listed in this file will be treated as a "0" towards the total rating. ARMORCLASS has a VALUE of -1 because lower is better, and so it needs to be flipped.
It appears this file can be appended with any stat in STATS.IDS along with a multiplier to make the engine consider that stat when recommending equipment.

In BG2EE we have:

2DA       V1.0
0
                VALUE
MAXHITPOINTS    1
ARMORCLASS      -1
DAMAGE_MIN      1
DAMAGE_MAX      1
AVERT_CRIT      1
MOVEMENT_SCALE  1
THAC0BONUSRIGHT 1