One big difference is the smaller the device, the quicker and cheaper it is to iterate. If it takes 15 years and $X billion to build and test your device, then

One big difference is the smaller the device, the quicker and cheaper it is to iterate. If it takes 15 years and $X billion to build and test your device, then progress gets measured on a per-lifetime instead of per-year basis. If your device can be built in a year and for $X millions instead, the testing and debugging can be done much faster. For a software dev comparison, think waterfall versus agile.