Very often I find myself having to run a find (or find and modify) operation on one collection, check the result, and then conditionally push an update or insert to a different collection. Constantly requiring two round trips to the database.

It would be incredible if you could batch these together. Execute a find or find-and-modify operation, then depending on a field or fields gathered, execute a secondary operation on a different (or the same) collection. Maybe even feed the find result into the secondary operation (but that would be asking a lot, haha).