Energy system planning is a difficult task, since it involves long-term decision-makings with multiple dimensions: technical, economic, social, ecological, and political. The rise of distributed and multi-energy systems including new technologies has further increased this complexity. Techno-economic studies based on optimization models have recently received much attention in the literature. They are essential to grasp energy systems complexity and provide decision support. This work targets methodological issues related to local systems while comparing them with methods used at larger scales. First, a new framework providing a comprehensive vision of added values and limits of optimization models is presented. Then, the main methodological trends as well as several undertaken research paths are identified based on the analysis of more than 60 research papers. The review results are summarized in a complete and concise table. Finally, future research topics are discussed including the operational facets of investment optimization models in case of high intermittent energy shares, flexibility issues and long-term operational decisions. The results provide useful information to modellers or researchers that look for appropriate and state-of-the-art optimization methods, or aim to deepen current research paths. Hence, they will facilitate the planning and development of energy systems for the future.