The first of PMI's five knowledge areas of portfolio management is the Strategic Management of the portfolio and this for good reasons. Without the highlevel input it is impossible to create the portfolio management plan and without a plan, well it is clear that all the activities within the portfolio management are lacking of focus. In the best case the work of the portfolio manager is only inefficient, wasting time on the project request that at the end get no support and disappear in the "hall of never started projects". 

In the worst case the portfolio management is seen as only overhead and not delivering a single value to the organization. He or she is then more administrating the portfolio than managing it.

The collection of strategic input will provide the following benefits

• Guidance: A clear vision of what is important to the organization will already reduce the number of new submitted project requests and this avoids that unnecessary work is performed on things that doesn't add any value to the portfolio
• Value: The strategy and derived priorities are the basis to evaluate the project requests and pick the best one to become project candidates. The criteria for evaluation must be public, the evaluation process 100% transparent. Otherwise you are loosing 
• Measurement: Only having a strategy enables you as portfolio manager to measure the success of your portfolio against the overall roadmap of the organization. Here is the area where you can demonstrade your value that you are delivering to the organization

Important is that the strategy is known so you should ensure that it is included in your portfolio management and your portfolio communication plan.