Simply put, product management organization leads the What and Why at the beginning of the product. The When part is a continuous iterative process to define, refine and redefine the product features based on the adoption. Clearly, development teams needs autonomy on How part of the feature building and serviceability phase. Product managers solve customer problems in this process.
In other words, product management org helps the organization by partnering with engineering org to build a product that solves a customer's need to make sure that it's economically viable. By doing so, the product management organization increases the chances of product success in the market. Lastly, product manager avoids to create a great product that no one uses.