Where is the $project stage typically located in an aggregation pipeline?

The $project stage in an aggregation pipeline is primarily used to shape the documents that are passed through to the next stage. It specifies which fields should be included in the output documents and can also be used to create new fields or reshape existing ones.

Placing the $project stage last in the aggregation pipeline is beneficial because it allows you to refine the output once all necessary transformations and computations have been performed. By the time the pipeline reaches the $project stage, you may have already filtered, grouped, or sorted your data. At this point, it becomes most efficient to select the exact fields you want to output, ensuring that your final results contain only relevant data while possibly reducing document size.

The typical usage of the $project stage at the end, focused on the final output, makes it easier to tailor results with precision and clarity, which is why that placement is considered the most appropriate.