To limit the probability of insufficient support for flat insulating concrete form foundation walls, which could lead to an inability to support lateral earth loads, which could lead to movement of the walls, which could lead to concrete cracking or displacement of the 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.