The performance of the distribution system has mainly depended on the electrical losses and voltage regulations in the system, which directly influence the system reliability, energy efficiency and economic sustainability. Traditional approaches like capacitor banks, feeder reconfiguration and on-load tap changers (OLTCs) have been used to address these issues but the performance of these techniques remains a concern when they are subjected to dynamic load conditions, renewable integration and complexity of the modern grid operations. The emergence of advanced techniques like mathematical optimization, metaheuristic algorithms, artificial and machine learning, distributed generation, smart grid architectures and Flexible AC Transmission System (FACTS) have addressed these issues in an effective way. This paper presents a systematic review between the years 2020 to 2025, on the existing approaches and compares the traditional and modern approaches in terms of loss reduction and voltage regulation. This review further focuses on the strengths and weaknesses of the optimization methods in order to improve the power quality in the distribution systems and also the integration of the data-driven intelligence in the smart grid contexts. It also highlights the key challenges like scalability, uncertainties and gaps between the simulation results and real-world deployments. This review further outlines the future directions and majorly highlights the potential of the hybrid optimization frameworks, explainable AI, FACT designs, Adaptive capacitor banks designs.