To limit the probability of insufficient reinforcement around openings or that reinforcement around openings will not be adequate to ensure a bond develops between the concrete and the reinforcement, which could lead to loads not being transferred across openings, 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.