To limit the probability that inappropriate grades of visually graded lumber will be used, which could lead to compromised structural integrity of the visually graded lumber or of elements supported by the visually graded lumber, which could lead to excessive movement, deformation or failure under expected lateral, gravity or wind uplift loads.
Where lumber is used in assemblies that are required to provide fire resistance, this is to limit the probability of the compromised fire resistance of the assembly, which could lead to harm to persons.