To supersede the requirement in Sentence 2.4.9.3.(1) for minimum fixture outlet pipe size, where fixture outlets serve multiple compartments of the same sink that might be drained simultaneously and for which the hydraulic load is likely to be higher, but not likely to be as high as would be imposed by separate sinks.
This is to limit the probability that inadequate size will lead to an inability to drain multiple sink compartments simultaneously, which could lead to a backup, which could lead to unsanitary conditions, which could lead to harm to persons.