To limit the probability that masonry units without voids or flashing will be incorrectly installed, which could lead to discontinuity between the materials installed to control the infiltration of soil gas in a floor-on-ground and the dampproofing (which serves as protection against the infiltration of soil gas) on the exterior of the masonry wall, which could lead to the infiltration of soil gas, which could lead to negative effects on the air quality of indoor spaces.
This is to limit the probability of harm to persons.