Making sketches of real-life people improves not just the rendering and sketching skills but also improves the observation skills as well. For us architects and designer sketching serve an important tool to convey our designs and concepts and act as a medium to bring ideas to life. Moreover, one learns to pay attention to minute details which otherwise is easy to miss. Furthermore, sketching itself is a very calming experience which helps the mind to unwind.
The entire exercise was based on making sketches of yourself and people around you; their faces and body poses and rendering them and capturing their form as well as possible. Their organic unadulterated features help us to understand the natural beauty of a human and appreciate its proportions and natural features. Further, this helps us to understand and create the spaces that we as humans inhabit.