"How can the implementation of Just$-$In$-$Time $($JIT$)$ inventory management systems impact the operational efficiency and overall performance of a manufacturing company? Discuss the potential challenges and benefits associated with JIT, including its effects on inventory holding costs, production lead times, supplier relationships, and quality control processes. Consider the role of information technology in facilitating JIT implementation and the importance of organizational culture in sustaining its effectiveness. Finally, analyze how external factors such as market demand variability and supply chain disruptions may influence the success of JIT strategies in different industries."