The Elevator Problem

In some buildings, all of the elevators can travel to all of the floors, while in others, the elevators are restricted to stopping only on certain floors. Why? What is the advantage of having elevators that travel only between certain floors?

Suppose a building has five floors (1-5) that are occupied. The ground floor (0) is not used for business purposes. Each floor has 60 people working on it and there are three elevators (A, B, and C) available to take these employees to their offices in the morning. Each elevator takes approximately 25 seconds to fill on the ground floor. The elevators then take five seconds to travel between floors and 15 seconds on each floor on which they stop. If everyone arrives at approximately the same time and enters the elevators on the ground (0) floor, how long will it take everyone to get to work? How should the elevators be organized to get the employees to their offices as quickly as possible?