Эффект — желательное или нежелательное последствие реализации проекта, полученное в ходе использования его выходных результатов (deliverable). Задача балансирования программы проектов заключается в том, чтобы суммарное воздействие всех негативных и позитивных эффектов, полученных от реализации проектов в составе программы, привели к получению выгоды (benefit).

PMI Glossary:
The primary difference between projects and programs is based on the recognition within programs that the strategies for delivering benefits may need to be optimized adaptively as the outcomes of components are individually realized. The best mechanism for delivering a program’s benefits may initially be ambiguous or uncertain. Outcomes delivered by a program’s components contribute to the delivery of the program’s intended benefits and, as necessary, to refinement of the strategy of the program and its components.

Projects deliver outputs in the form of products, the use of which results in changes in the business. These changes are called outcomes. These outcomes allow the business to realize the benefits that are set out in the business justification for the project. Here’s an example of output, outcome and benefit:
Output: New sales system
Outcome: Sales orders are processed more quickly and accurately
Benefit: Costs are reduced by 10%, sales increased by 15% and revenue increased by 10% annually.