If you have a vehicle with no possible rear view out the back, you will find that the rear facing video camera are wonderful.
Also, a lot of folks are also mounting a 2nd video camera on the back of the boat and then using a split screen in the cab to be able to both see the front of the boat as well as what is behind the boat when backing.
With mirrors, it is impossible to see what is directly behind the truck or what is directly behind the boat. But rear facing video cameras with an appropriate video display solve the problem.
For example:
https://gearjunkie.com/gmc-transparent-trailer-view