Consider the lowly impression and the number of times there is a chance for an impression to go wrong. That is for it to distort or in some other way betray us from the moment it is taken until the restoration is ready to deliver.
Each of these materials; the impression materials, the stone, the wax, the investment and finally the metal has some sort of setting and shape change with time, temperature and moisture. Then there could be mechanical distortion if the tray bends, the die is abraded, the material compresses or is pulled slightly from the tray. And of course there are bubbles, contamination and tears.
Any one of these errors, lurking like little gremlins, can easily go undetected for at least a portion of the restoration fabrication process. The result…remake.
When you take a digital impression you eliminate all of those chemical and mechanical gremlins. The result is better and more reliable restorations with almost no remakes. In fact a study from iTero shows a remake rate of 0.3%