Visualization is very important to get the technique to work correctly. You will not have too many opportunities to spar and correct things in real settings. Other times one simulates. This to train the frontal lobe of the brain to be fully prepared. I know fighter aircraft pilots simulating the flight trajectory with their hands before beginning a sortie. During my Karate days I was always at a loss off as to why they. at least at my school, did not emphasis Bunkai. Bunkai is the visualization of the Kata, one of the many possible interpretation. All this takes away random responses and converts them into a credible strategy.