To limit the probability of inadequate capacity, rigidity or withdrawal resistance, which could lead to premature failure of nailed joints, which could lead to compromised strength of wood members, which could lead to an inability to resist expected vertical or lateral loads, which could lead to fastened elements detaching from supporting members.
For floors and elements supporting floors, this is to limit the probability of:
This is to limit the probability of excessive deflection or vibration, which could lead to persons losing their balance, tripping or falling, which could lead to harm to persons.