Look at it this way. Most of the time, the recording camera won't be started or recording when the car is in reverse, so it can't provide documentation in the case of an "event". All the rest of the time, it's recording a view that's not particularly useful. So it's money spent for something of little value. Not to mention the additional processor load it incurs. I can't emphasize enough that THAT is the biggest issue you have to deal with when running multiple cameras
. As someone who's used multiple cameras for some time now, once the novelty wears off, you'll just find yourself using one high-quality front view most of the time.