Product management versus portfolio management and how do you balance features requested, wanted, needed in a product with features requested, wanted or needed in another product in your portfolio of products? This is an art on the human level and a science on the business level. Product teams have their blood, sweat and tears invested in the product they own and work on, which makes the human aspect something to build into the portfolio management process. Another human aspect is customer service and sales who are dealing with existing customers and prospects. If only that one feature gets added their lives would be so much easier.
Then there is the science of what product and what feature will bring the new customers, the extra revenue, the reduction in R&D costs, etc. That all comes down to the profitability and future of the company.
It is a mistake to do product management separate from portfolio management. Product management should lead to a product business plan and roadmap which than needs to be aligned with all other products and decision made across the portfolio. There can only be 1 priority 1 feature in the company, 1 priority 2 feature, etc.
Re-arranging R&D teams, timelines, management customer expectations and much more are all part of portfolio management.