For coarser soil types near the footings' bearing surface (for which free water between soil particles can reduce bearing capacity), to limit the probability of excessive soil subsidence, which could lead to the cracking of foundations or building superstructures.
This is to limit the probability of:
For floors and elements supporting floors, this is to limit the probability of excessive movement, deflection or vibration of floors, which could lead to negative effects on the psychological well-being of persons.