Nothing compares to the lessons you learn watching yourself fight full contact on video.
Training is made up of pieces, some of this, some of that, and the endless progression of challenges. Heavy contact has to be part of your training, sometime in your career, and tournaments are a convenient and rather safe place to exercise.
By the grace of God, should you be lucky enough to never have to use your art, but if you do you'll benefit from those lessons undoubtedly.
Gene also makes a great point, with skill comes confidence to exercise a number of non-combative strategies to diffuse a potentially bad situation. It comes down to experience.
Guangzhou Pak Mei Kung Fu School, Sydney Australia,
Sifu Leung, Yuk Seng
Established 1989, Glebe Australia