Mechanical power systems frequently determine whether a certified high-performance building operates as intended after handover. Pumps, fans, chillers, boilers, heat-recovery devices, variable-speed drives and their control sequences form an interacting network in which small calibration errors can create persistent energy waste, unstable comfort and premature equipment wear. This review examines how commissioning and retro-commissioning can optimise those systems in LEED-certified buildings by connecting design intent, functional verification, operational data and corrective action. A structured integrative review was undertaken across peer-reviewed studies and current technical guidance published from 2020 to 2025. Evidence was synthesised around five themes: verification of design and installation, hydraulic and air-side optimisation, control-sequence validation, fault detection and diagnostic analytics, and measurement and verification of realised outcomes. The review finds that the strongest programmes treat commissioning as a lifecycle performance-management process rather than a close-out inspection. Effective strategies combine owner requirements, basis-of-design traceability, calibrated testing, trend-data analysis, seasonal verification, operator training and post-occupancy persistence checks. Retro-commissioning is valuable where simultaneous heating and cooling, excessive static or differential-pressure setpoints, failed sensors, unstable staging and schedule drift have accumulated. However, savings claims remain sensitive to baseline quality, weather normalisation, occupancy change and incomplete submetering. The paper develops a practical framework that prioritises interventions according to energy, reliability, indoor environmental quality and implementation risk. It concludes that commissioning produces durable value only when its findings are converted into controlled sequences, verified setpoints, accountable work orders and an ongoing evidence loop supported by competent operators.