Context
External PR: https://github.com/mongodb/mongo-go-driver/pull/1479
any insert operation preemptively generates new ObjectID to check/ensure if _id exists in doc or not - but chances are that goes to waste. this waste is more pronounced in scenarios where _id is a mix of custom userland id and system generated one across collections of a db or even across documents of same collection
Definition of done
What must be done to consider the task complete?
Pitfalls
What should the implementer watch out for? What are the risks?