Triggers in MongoDB can be implemented through application-based or oplog/change stream-based approaches. Application-based triggers are self-implemented and offer more flexibility but require additional development. Oplog/change stream-based triggers allow monitoring database operations by tailing the oplog or using change streams. Considerations for oplog/change stream triggers include handling rollbacks, maintaining operation order, and filtering migration/orphan events in sharded clusters. An example use case is analyzing shard keys by monitoring operations on a collection to identify access patterns before defining the shard key.