Draping on a live model.
I have done that once or twice when the body in question was quite disproportionate and I felt that I would get a better result more quickly than flat pattern drafting and then making a mock up.
Draping is very informative for sure. Once you have a drape, you need to make it into a paper pattern and it does help to know something about how patterns are flat drafted so you can make small adjustemnts as necessary because fabric is easily distorted in draping. It is good to use a large check fabric as they have done as it shows when you have pulled too much one way or another.
That model has a very long neck doesn't she?it is also interesting to notice the small disproportions that everyone has, one shoulder lower, one hip higher etc.
Thanks for sharing that video.