When running aggregate explain with verbosities "executionStats" and "allPlansExecution", the output will include "nReturned" and "executionTimeMillisEstimate" for each aggregation stage.
Description of Linked Ticket
For the same reason explain exists for .find(), it would be helpful to know how long an aggregation pipeline takes to run and within each stage. In many ways it is even more important with .aggregate() because of potentially multiple pipeline expressions for the same result.
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