This file would define which spells are given to priest and mage classes on level-up. With the default file, priests gain spells SPPR[1-9][**] and mages gain spells SPWI[1-9][*8] where ** is the column from this file. However, this file is not actually used by the engine, the amounts are hard-coded to 50.

In BG2 ToB we have:

2DA V1.0
0
            1       2       3       4       5   6	7
MAGE        50      50      50      50      50	50	50
PRIEST      50      50      50      50      50	50	50