The incorporation of graphene into cellulose matrices has emerged as a promising strategy for enhancing the structural and functional properties of composite materials. This comprehensive review provides a critical analysis of recent advances in optimizing graphene content in cellulose matrices and its impact on composite performance. Various optimization techniques, including response surface methodology, particle swarm optimization, and artificial neural networks, have been employed to identify optimal graphene concentrations and processing conditions. Quantitative analyses demonstrate significant improvements in mechanical properties, with notable increases in tensile strength and Young’s modulus reported for graphene/microfibrillated cellulose composites. Substantial enhancements in thermal stability have been observed in lysozyme-modified graphene nanoplatelet–cellulose composites. Electrical conductivity has been achieved at low graphene loading levels. Additionally, barrier properties, biocompatibility, and functionality for applications such as energy storage and environmental remediation have been substantially improved. This review explores case studies encompassing the optimization of thermal conductivity, viscosity, durability behaviors, pollutant removal, and various other properties. Despite promising results, challenges remain, including uniform dispersion, scalability, cost-effectiveness, and long-term stability. Strategies such as surface functionalization, solvent selection, and protective coatings are discussed. Future research directions, including novel processing techniques like 3D printing and electrospinning, as well as the incorporation of additional functional materials, are outlined. This review synthesizes current knowledge, identifies emerging trends, and provides a roadmap for future research in the rapidly evolving field of graphene–cellulose composites.