To limit the probability of insufficient vertical reinforcement or that the vertical reinforcement will not be adequately encased and bonded to the concrete, or will be unable to support lateral earth loads, which could lead to concrete cracking or the displacement of foundation walls.
This is to limit the probability of:
For floors and elements supporting floors, this is to limit the probability of excessive deflection, which could lead to rough or uneven walking surfaces, which could lead to persons tripping or falling, which could lead to harm to persons.