We have some slow large aggregation pipelines where a $limit at the end is not sufficient to prevent slow queries, and where a $limit early in the pipeline would give incorrect results.

Hence we want to have a way to limit early but abort the query instantly if this limit is hit:

For example:

aggregate([
   { $match: {....}},
   { $imaginaryNewAbortOnCondition: { 
        count: {$gt: 100}, 
        message: "Too many rockets found, please limit the search range"
     }
   },
   { $lookupUnwindOrOtherExpensiveAggregations: {...}},
   { $limit: 100 }
])

I think limit is our main use case but one could also imagine other uses where a more dynamic condition is useful.