The purpose of computers is to do the work we don't want to do. Traditional crossword puzzle numbers exist only to associate grid squares with certain across or down clues, and vice versa. For all practical purposes, you don't have to use numbers. You could use letters or symbols just as well. Or mouse clicks.
Computers can associate clues with grid entries immediately and flawlessly.
Click on any grid square in a Crossdown puzzle and the right clue appears. Click on any clue in the clue list and the right grid entry word is highlighted. With printed puzzles, the numbering is often so small or blurry it is easy to read the wrong clues and make big mistakes. This can never happen with Crossdown. And Crossdown is easier on your eyes.