To limit the probability that penetrations of a fire separation will not be sealed or cast in place, which could lead to a failure of the integrity of the fire separations, which could lead to the spread of fire and smoke from one fire compartment to another fire compartment, which could lead to harm to persons in the other fire compartment.
To limit the probability that fire will spread into the fire-rated assembly through the protecting membrane, which could lead to the premature collapse or failure of the assembly, which could lead to harm to persons.