Whilst this may make PM purists shudder, I can think of many examples in my career where the PM has also been the PD and this was the right approach. When I look over my old requirements documents, clearly I defined some of the how, especially when the engineering team's knowledge of the product/solution space was limited, customers had specific requirements, or we didn't have anybody else to perform this role (i.e. no architect assigned).
However, organizations reach a point where evolution of their products and business can no longer be sustained by a single product manager/product designer (PM/PD). Usually this is because the single person acting as the PM/PD no longer scales - the business has grown to be too complex or the product too complicated for one person to handle. Too often this person often ends up becoming the bottleneck in the product development process.
Organizations attempt to solve this problem in two distinct ways:
- Some organizations hire another PM/PD - this works temporarily, but usually it isn't sustainable long-term since there are relatively few people who are actually capable of being a PM/PD. Most companies also find that they can't hire an external PM off the street to be an effective PM/PD since that new person simply won't have the in-depth product knowledge or historic context to be successful. Even if these problem can be overcome, the bigger issue with this staffing approach is that it tends to breed a cadre of feature-driven product managers/product designers who ultimately lack business and strategic vision.
- The other approach, which I believe is ultimately more successful, is to begin to delegate PM/PD responsibility and then scale across the functions. This delegation can occur in a number of different ways. The PM/PD can become either a business and market focus product manager with the technical responsibilities farmed out to a technical product manager, product architect, or dedicated product designer. Or, the PM/PD becomes the technical product manager and is backed up by a business-focused product manager.
In my experience, I've seen the first approach to product management and product design stall the organization; it becomes increasingly difficult to grow the business beyond a certain size or gain a strategic focus. The latter approach (delegating roles) tends to be much more scalable and sustainable. Microsoft, Symantec, certain divisions of Citrix, Cisco, and other blue chip technology companies all tend to organize their product managers along the delegated approach. Titles may be different depending upon the company (Program Manager & Product Manager at Microsoft vs. Technical Product Manager & Product Manager at Cisco and Symantec vs. Product Architect and Product Manager at Citrix), but the associated roles and responsibility are essentially similar.