Without minimizing the contribution of other departments, of which there may be as many as ten or more, the bottom line is if there is no engineering department there is no hotel. Take away those services like hot water or elevators, heating or cooling, electricity, kitchen equipment, laundry equipment etc, you simply would have no customers. When everything is working the next most significant department of course is housekeeping whose efforts keep the property clean and attractive, tending to the guests comfort in their rooms. Removing a restaurant from the system will not close the hotel, or closing the bar or lounge will not cause the hotel to cease operations. Again, all departments should contribute to a seamless operation where the guest comfort and safety and satisfaction are paramount.