Some older theories of business cycles-usually associated with the "Austrian" school of economics- claimed that recessions and depressions were useful in helping to remove the poison from an economy that builds up during good times. For example, weaker companies are the first to go when the demand for an industry's product falls during recessions. Employees who are allowed a lot of slack during good times are forced to work harder during recessions in order to keep their jobs.
The overinvestment vs malinvestment confusion can be clarified by reading these essays.
That the recession is unavoidable is the crux of the matter, and not obvious at first. Mises provides a parable with house builders to illustrate this idea. It is presented in a simple fashion here.
The one good thing about the bust is that people start having realistic expectations. It is useful in that it allows them to start projects which are moke likely to be successful. Had their expectations remained unsustainable due to the monetary distorsion of relative prices and interest rate, they were likely to fail en masse.
The recession is also "good" unless one considers that production should not meet consumer preferences. This would be the case if no adjustments took place in the allocation of labor and investments. These adjustments have no reason to take much time. But if a major recession is defined as an extended period with more than 9% unemployment, this is an entirely different issue. Any definition is acceptable as long as we know which one is being used.