In any field, good training is important. Whether one is training to become an astronaut or a race car driver, the quality of that training will have an impact on the overall effectiveness and ability of the person afterward. Part of that training is putting the trainee in realistic situations so that they can practice real-world scenarios. Take astronaut training. Astronauts will practice procedures in pools to simulate low-gravity. So approximating real-life conditions is important. And in medical training, the same obviously applies.
However, in medicine one is faced with the challenge that not every doctor-to-be will have the opportunity during their schooling to encounter every type of illness or physical condition. So rather than leave that as an area that the student has only read about or seen in books, moulage and medical manikins exist.
Moulage is a form of makeup, where a live person or a dummy can be made to look like they have a certain disease or injury. Manikins are mock-ups of bodies (or parts thereof) that can be used to practice certain procedures. Take a Susie Simon manikin for example. It comes with a variety of realistic parts offering students a chance to practice and experience a wide range of medical procedures.
Other manikins exist that specialize in specific areas of the body, like dental or birthing manikins. Others still specialize in only one specific procedure. While they may be limited, they still offer an unparalleled level of realism for practice.
The better the medical training is, the better we can expect future doctors to be. So it makes good sense to invest in developing better tools for this endeavor. After all, everyone is going to have to see the doctor at some point, and when you do, you want them to be as competent as possible.