To limit the probability of ice lens formation beneath foundations that are installed on fine-grained soils (which can retain quite a bit of water), which could lead to the excessive vertical movement of the soil, which could lead to excessive stress on foundations, which could lead to structural damage to foundations and superstructures.
For floors and elements supporting floors, this is to limit the probability of excessive deflection or damage, which could lead to rough or uneven floor surfaces, which could lead to persons tripping or falling, which could lead to harm to persons.