There is a partial myth about training and learning that suggests that learners must be active in the sense that they should be "doing something" that can be seen. The notion is that if they are not doing something that can be seen, they are inert, and therefore not learning.
The significance of modeling / observational learning goes beyond its power as a training and learning tool, but it affects our understanding of this myth. The work of Bandura and subsequent huge body or research material tells us that people learn tremendous amounts by watching others, essentially a seemingly passive "activity". Not only are physical skills learnable through observational learning, but behavior commonly related to attitudes can also be affected by the observing of how others behave.
This provided valuable and sophisticated learning and teaching tools to trainers that do not require learners to be "doing something" all the time.
That's not to say that modeling is a stand alone training technique. It works best as part of an instructional system that provides opportunity to practice, and some other components.