The complex nature of today’s business world, characterized by technological disruption, market volatility, and stringent regulations, necessitates sophisticated solutions to navigate successfully. One such solution is the engagement of project management consultants, professionals who bring a wealth of knowledge, experience, and expertise to ensure optimal project execution.

The first compelling reason to bring these consultants onboard is their capability to provide a fresh, objective perspective. Just as authors occasionally need editors to refine their work, companies can benefit from an outsider's insights and impartial advice. Project management consultants are not ensnared in organizational politics or culture, enabling them to identify inefficiencies, suggest improvements, and instigate change without fear or favor.

Another reason is their proficiency in specialized knowledge and skills. As Pareto's Principle suggests, 80% of a project's success can be attributed to 20% of its activities. The challenge lies in identifying that crucial 20%. With their extensive training and experience, project management consultants are adept at discerning these activities, applying best practices, and averting common pitfalls.

Thirdly, they bring a level of agility that is essential in the current business climate. With their grasp of iterative methodologies like Agile and Scrum, consultants can expedite the project lifecycle while maintaining flexibility. They respond swiftly to changing needs and unanticipated obstacles, minimizing time delays and cost overruns.

The fourth reason lies in the sphere of risk management. Nassim Taleb's 'Black Swan Theory' underscores the profound impact of rare and unpredictable events. Project management consultants are skilled in anticipating, preparing for, and mitigating such events, thereby ensuring business continuity and resilience.

Fifthly, consultants offer a cost-effective solution for businesses. Engaging a consultant for a specific project eliminates the need for long-term commitments, providing financial flexibility. Moreover, the consequential improvements in efficiency and productivity often lead to significant cost savings in the long run.

The sixth reason pertains to stakeholder communication. As boundary spanners, consultants possess the diplomacy and tact to liaise between different stakeholders, balancing their varied expectations and interests. They ensure transparency and open communication, fostering trust and collaboration.

Lastly, consultants facilitate capacity building within the organization. By working closely with the internal team, they impart invaluable skills and knowledge, enhancing the team's capabilities long after the project’s completion.

However, leveraging these benefits necessitates careful selection of consultants. It's essential to verify their credentials, track record, and compatibility with the organization's culture. The opportunity cost of a poor choice can be significant, leading to wasted resources and potential project failure.

In conclusion, the engagement of project management consultants can provide a strategic advantage in today's cutthroat business environment. Their objectivity, specialized expertise, adaptability, risk management skills, cost-effectiveness, communication prowess, and capacity-building potential make them a valuable asset. However, their selection should be approached judiciously, keeping in mind the organization's specific needs, objectives, and culture.