To limit the probability that persons using exits will not be familiar with assigned floor numbers, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.
To limit the probability that a person with a visual impairment [or disability] will be unable to determine the floor number by reason of being unable to reach raised numbers and feel them, which could lead to delays in the evacuation or movement of persons to a safe place, which could lead to harm to persons.