Lets draw an analogy of a human body. Our body needs to maintain a constant temperature of 98.4 F to work effectively. Even a minor increase or decrease in body temperature can lead to further deterioration of one or more body parts.
Similarly, most Electrical types of equipment require a constant voltage supply of 400v to last longer & run efficiently. Electric motors draw considerably high at high/Low voltage, causing excessive power losses and resulting in their premature failure. Similarly, Bulbs/Tubes/luminaries could consume up to 40% more power at high voltage and may last for a mere 10% of their normal life.