The text discusses two performance optimizations for Couchbase 2.5.1 and below, which affect reading and writing operations in the cluster. These changes should only be made with properly sized clusters to avoid problems. The first optimization involves adding more reader/writer threads per bucket, allowing more operations to be performed. The second optimization optimizes Couchbase for mixed usage or write-heavy workloads by adjusting workload optimization settings using a REST API call. Additionally, changes require a restart of the bucket to take effect, and it is recommended to plan accordingly for downtime. However, these optimizations are no longer necessary in Couchbase 3.x due to the introduction of the Global Thread Pool, which dynamically manages threads and balances them according to workload intelligence.