What does a Project Manager Do?
In order to achieve control, there must be a plan. It is the Project Manager who plans the sequence of events to deliver the project. This can be thought of as being akin to a conductor in an orchestra, who doesn't necessarily play all the instruments but is well versed in their subtleties and capabilities and knows who should be playing what and very importantly when.
The Project Manager delegates the tasks with the intention that everything should "go to plan". However, this cannot always be relied upon and it is therefore the Project Manager's responsibility to monitor how well the work in progress matches the plan. If the work does not match the plan, the Project Manager has to do something about it - either positively (i.e. an opportunity to save time/money) or negatively (e.g. taking corrective action).
The intention is to make the right information available at the right time to the right people to make the right decisions.