Monitoring MongoDB performance with the WiredTiger storage engine requires tracking various metrics to ensure high availability and efficient resource utilization. Key areas to focus on include throughput metrics, database performance, replication and Oplog, journaling, concurrent operations management, cache metrics, errors, and scaling MongoDB using sharding or replication. By monitoring these metrics, you can quickly spot slowdowns, hiccups, or pressing resource limitations and take corrective actions before they impact user-facing services.