An application portfolio assessment is a process of evaluating and analyzing an organization's collection of applications, commonly known as the application portfolio. It involves reviewing the applications and assessing their business value, performance, dependencies, and alignment with the organization's goals and objectives.

Application portfolio assessment is crucial because it helps organizations understand the current state of their application landscape and identify redundancies, vulnerabilities, and opportunities for optimization or modernization. It provides insights into the overall health of the application portfolio and enables informed decision-making regarding future investments, rationalization, and migration strategies.

Application portfolio assessment provides critical information for effective portfolio management. By evaluating and analyzing the application portfolio, organizations can identify areas for consolidation, rationalization, or migration, resulting in improved efficiency, reduced costs, and enhanced alignment with business objectives.

Application Portfolio Management is the practice of managing a company's portfolio of software applications to optimize their performance, lifecycle, and business value in alignment with the organization's enterprise architecture and strategic business objectives. 

APM is considered a best practice for enterprises because it enables them to effectively manage their application landscape by identifying redundant or underperforming applications, aligning technology investments with business capabilities, and maximizing the business value derived from their software assets.

The key objectives of effective APM include optimizing the total cost of ownership of the application portfolio, aligning technology investments with business needs, improving business processes through rationalization and lifecycle management, and enhancing business capabilities through strategic portfolio management. 

Best practices in APM include using specialized APM tools to facilitate portfolio analysis, establishing a transparent management process for application rationalization, developing a clear roadmap for optimizing the application portfolio, and engaging stakeholders to align APM efforts with business goals. 

Organizations can optimize their application portfolios by regularly assessing each application's business value and effectiveness, prioritizing applications based on their strategic importance, rationalizing the portfolio to eliminate redundancy, and implementing governance mechanisms to ensure ongoing optimization. 

Enterprise architects play a crucial role in APM by providing strategic guidance on technology investments, defining the architectural principles that govern the application portfolio, and ensuring that the portfolio aligns with the organization's enterprise goals and objectives.