Answer:
Generally companies engage in massive layoffs because economic times are hard, but evidence show that massive layoffs actually do not benefit companies, instead it hurts them in the long run.
According to a study made by the Harvard Business Review, 45% of Fortune 500 companies carried out layoffs on a normal basis and 65% did it during the great recession. But that didn't help them become more profitable, nor more productive. Actually, the study showed that companies that engage in massive layoffs suffer financially for at least 3 years after the layoffs have been made. Remember that layoffs in America are rather simple and cheap to do, the negative effects of layoffs last longer in countries where firing people is expensive.
Most companies start firing employees because things are not going well and they are used as a way to cut costs. But even though firing people in the US is not expensive, hiring and training new employees is. Some companies like Toyota or Honda rarely fire anyone. Toyota aversion for layoffs is so great that it hasn't manufactured any cars in Venezuela for more than 7 years already, and it hasn't fired any employee. It rather relocated them to other countries after receiving more training.
Massive layoffs result in lower job satisfaction, organizational commitment and overall job performance. So any money saved by cutting jobs is lost by lower efficiency. Some universities have pointed out that the negative effects of massive layoffs can last up to 20 years. Remember that people are involved, not machines. When people feel disappointed and betrayed they will not behave in the same way. Negative effects tend to last much more than positive effects, e.g. wage increase which is seem as natural and fair.
What can be done:
Think like Toyota. If you know that X number of employees will not be needed in the future, retrain them and transfer them to areas where they can be useful. E.g. AT&T engages in a massive retraining policy for future unnecessary employees and managed to relocate 100,000 of them in 7 years. That actually boosted AT&T's productivity, increased its revenues and decreased costs. They were able to retain talent and boost morale.
When laying off employees is unavoidable and unforeseeable (which is rarely the case), companies should offer their employees a fair way out. They should also avoid making other remaining employees feel uncomfortable or that they are next in line to be laid off.