Agent-based crowd simulation in virtual environments is of great utility in a variety of domains, from the entertainment industry to serious applications including mobile robots and swarms. Many studies of crowd behavior simulations do not consider the fact that people tend to congregate in smaller social gatherings, such as friends, or families, rather than walking alone. Based on a real-time crowd simulator which has been implemented as a unilateral incompressible fluid and augmented with group behaviors, a perceptual study was conducted to determine the impact of groups on the perception of the crowds at various densities from different camera views. If it is not possible to see groups under certain circumstances, then it may not be necessary to simulate them, to reduce the amount of calculations, an important issue in real-time simulations. This study provides researchers with a proper reference to design better algorithms to simulate realistic behaviors.