To supersede the requirements of Sentences (3) and 9.9.4.2.(1) by waiving the requirement for the fire separation to have a fire-resistance rating, if certain conditions are met [i.e. lobby and adjacent occupancies are sprinklered].
This is to limit the probability that a fire will spread into the lobby from an adjacent occupancy, which could lead to untenable conditions in the exit, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.