Pedestrian simulation is a consolidated area of application in which agent-based models are often employed; successful case studies are described in the literature and commercial, off-the-shelf simulators are commonly employed by decision makers and consultancy companies. Most state-of-the-art models, however, generally do not consider the explicit representation of pedestrians aggregations (groups) and their implications on the overall system dynamics. This work is aimed at discussing the relevance and significance of this research effort with respect to the need of empirical data about the implication of the presence of groups of pedestrians in different situations (e.g., changing density, spatial configurations of the environment). The article describes an agent-based model encompassing both traditional individual motivations (i.e., tendency to stay away from other pedestrians while moving toward the goal) and a simplified mechanism considering the cohesion effects related to the presence of groups in the crowd. The model is tested in a simple scenario to evaluate the implications of some modeling choices and the presence of groups in the simulated scenario. Moreover, the model is applied in a real-world scenario characterized by the presence of organized groups as an instrument for crowd management. Results are discussed and compared to experimental observations and to data available in the literature.