By using this button 
, you open a Planning board that is linked to the priority planning window, and which can be used to see a general overview of several work centers regarding the time and quantity for ready to run operations, as well as upcoming operations and operations in progress.
This board can also be used to quickly switch work center in the priority planning, which is done by just clicking on the desired work center in this window.
Another handy feature is that you can "drag and drop" an order number in the priority plan to a work center in the Planning Board in order to change work center on the operation.
The help document for the Planning Board provides a more detailed description.