Optimization problems in energy planning are often tackled using Mixed Integer Linear Programming (MILP) models. While MILP formulations are renowned for their efficiency and reliability, the computational burden increases significantly with the number of integer variables, making detailed optimization impractical for large power systems. To address this challenge, energy planners frequently employ clustering techniques to select representative periods, reducing the problem's dimensionality. However, despite extensive research on clustering algorithms, there is not yet consensus on their application in energy planning; their accuracy, potential limitations, and alternative solutions. This paper aims to provide new relevant insights on the subject. Building on existing literature, we examined several multivariate time series clustering methods, including hierarchical, fuzzy, and k-means clustering, using both centroid and medoid representations for cluster centers. The analysis incorporates the most common technologies used in modern power systems, such as solar, onshore and offshore wind, and storage systems (i.e., Battery Energy Storage System-BESSand hydrogen). The paper also includes a numerical example of a capacity expansion plan, utilizing the PyPSA tool.