What is a advantage of good managers?

What is a advantage of good managers?
There was a book written many years ago entitle "Made In The USA" or "Made In America" which suggested that 80% of the problems in business was management not the employees. Employee tend to be willing to do whatever they need to do to get the job done. Employers/management and hence managers often times throw up as many barriers as anything when running the business. They have the wrong equipment to do the job. An employee works hard to achieve one level of performance only to have an even higher goal set. Managers are often not taught how to be managers. They are often someone who has lasted long than most and have somehow been able to be promoted. For instance, good engineer does not make for a good supervisor of other engineers. The main advantages of good managers is that those who are over them in the hierarchy can trust things are getting done and done well. At the same time, those whom they supervise can know that they are being treated well and fairly and therefore are more willing to do the work and feel less frustrated.