The biggest impact and value-add of a good Product Manager is strategic - laying out the overall business and product vision, identifying key needs, building a strong business case, defining the product, and Commercialization and Go-to-Market strategy.
Tactical tasks such as market research, user research, UX design, marketing collateral, and product operations are secondary functions for Product Managers.
When a Product Manager is not present from the start, others take ownership of key PM functions, leading to confusion when a new PM is hired.
One important function of a Product Manager is to envision the future with more clarity and detail than any other team member, painting an inspiring vision for the team and gaining alignment from stakeholders.