I think it is clear that project managers are expected to control their projects so that they meet their budget, schedule, scope, and performance targets. When you really consider it, that is a tall order, because what it really means is that you are supposed to control the performance of people so that they collectively achieve these targets. It is akin to the responsibility of a CEO or President of an organization, and Stafford Beer wrote a couple of books* in which he argued that this is only possible if you manage the law of requisite variety.
This law pertains to systems, and was expounded by Ross Ashby. It says that, in any system of humans or machines, the element in the system having the greatest flexibility in its behavior will control the system.
Now if you consider a project team to be a system of humans, this law is saying that the project manager can be in control only if s/he has greater behavioral flexibility than any other element in the system. The difficulty of doing this has been expressed in the description of project management as herding cats. As we all know, cats don't herd like cattle, so the implication is that project teams are very difficult to take to a desired destination, and this is indeed true.
It seems that many, if not most, managers recognize the difficulty, and they try to reduce the variability in the behavior of the project team with prohibitions, called policies at the organizational level. I call them the "thou-shalt-not" rules for project team members. And as Tom Peters argued in Thriving on Chaos, they simply do not gain compliance of organization members.
The proper way to reduce the variability of the project team turns out to be a part of the very procedures we should use when we plan and manage a project. You will remember that control is defined as follows:
Control is exercised by comparing where you are to where you are supposed to be, so that corrective action can be taken when there is a deviation from plan.
Now since it is the plan that tells you where you are supposed to be, it follows that if you have no plan, control is impossible--by definition!
So if you follow good project management procedures, you will not only have an overall plan, but every team member will have an individual working plan that is derived from the project plan, and if he/she is following that plan, she will be in control most of the time (and will know how to recover if she loses control momentarily), and if every member of your team is in control, then the project will be also. And this is the ONLY way in which you will ever have control of a project.
For that reason, it is absolutely imperative that you practice planning at the team and individual level. Otherwise, you will spend all of your time trying to herd all the cats in your team.
Notes*: Brain of the Firm and Heart of Enterprise are Stafford Beer's books. For a more extensive discussion of this, see my book, Project Planning, Scheduling, and Control, 5th Edition.