One argument is that the just-in-time, or JIT, discipline enables companies to cut inventory carrying costs even if that comes at the expense of the integrity of their supply chains. In other words, companies are said to be willing to sacrifice customer service in their pursuit of cost savings.

But much of the criticism stems from a misunderstanding of how the business strategy works and the benefits it can deliver in the production of goods.

The main focus of JIT, which was pioneered in the manufacturing sector by Japanese car maker Toyota Motor Corp. , isn’t simply to minimize inventory costs but to improve product quality. A system built around a carefully synchronized supply of components cannot tolerate a high level of defective parts or other quality-related issues.

The JIT system, then, highlights quality deficiencies, which are then corrected. And in doing so, it improves the manufacturing processes. Such improvements reduce inefficiency such as the need to retool components. Sales will also rise as manufacturing quality standards improve, reducing unit costs for production because more finished goods are sold and not returned to correct defects.

The case for buffer stock includes the argument that more inventory will make supply chains more resilient.

Certainly if there is one quality that needs improvement in supply chains, it is that they need to become more resilient. But JIT also reinforces resilience because it strengthens the relationships along the supply chain between companies, their suppliers and customers. Close relationships allow companies to react collaboratively to supply-chain disruptions.

Close relationships that are managed over time will promote agility, which the pandemic disruptions have demonstrated is a critical discipline in managing supply chains. A well-constructed JIT operation should be able to react quickly to unexpected shifts in supply or demand because it is not encumbered by large inventory volumes that must be dealt with and can distract planners from making needed adjustments.

When disruptions occur, the response speed can make the difference between locking up alternative capacity and losing production because the required manufacturing capacity is unavailable.

Buffer inventories certainly can help companies ride out short-term disruptions. But they won’t address long-term dislocations such as those inflicted by a pandemic.

Certainly companies are learning important lessons about how to manage inventories that might cause them to rethink how they apply JIT.

Indeed, Toyota itself went through such a review after the 2011 tsunami inflicted severe damage to manufacturing sites, leading to shortages of semiconductors and automotive components that were felt around the world. The company reviewed its global supply vulnerabilities and concluded that it needed to stockpile semiconductors owing to the long supply lead times associated with these components.

Toyota’s lessons enabled it to pass rival General Motors Co. in U.S. auto sales in the second quarter of 2021 for the first time, a trend that held up for the year.

However, its bigger stockpile didn’t give Toyota long-term immunity from pandemic-driven supply problems, and the company has cut production in recent months as its inventory of chips has dwindled.

The Toyota example underscores the need for a flexible approach to inventory management, with just-in-time a critically important tool in the toolbox. Even JIT-heavy companies often have substantial buffer stocks for certain materials and parts.

The discipline will certainly come under more scrutiny as experience with the impact of the past two years’ supply shocks grows.

For now, companies are building inventories to meet strong consumer demand. Over ordering of parts and finished goods is rife, and the impact is spreading through supply chains. This trend will halt when demand collapses, as it inevitably will, and companies will be saddled with bloated inventories.

When this happens, companies will again come under pressure to review their inventory-management practices. They should keep in mind that the benefits of just-in-time remain just as important now as they were before today’s disruptions, and should continue to guide well-designed supply chains in a post-pandemic world.

Yossi Sheffi is director of the Massachusetts Institute of Technology’s Center for Transportation and Logistics. His latest book is “A Shot in the Arm: How Science, Engineering, and Supply Chains Converged to Vaccinate the World.”