I think wifi consume resources, and so the cameras might use a lesser bitrate, at least that is how it is in some cameras.
It do also generate heat not least from the LCD screen.
The wifi stream also have a delay to it, not a massive one but it is there, also with wifi on that overrule the automatic start and stop recording features so you would have to remember to manual start recording every time you start your car and the camera have turned on ( with wifi on too )
stop recording i dont think are a problem when the wifi are on, if you stop the car with the wifi on i assume it just change to parking mode as normal.
Same as if you turn on wifi, the camera will stop recording, so if you are driving and still want to record you will have to start a new recording by pressing the REC button on your phone screen. ( unsure if you can also use the camera REC button at this time )
I know its a new toy and all, but really you are best off if people dont know the cameras are there, and a LCD screen going will signal that.
Also in Denmark at least it might be illegal to have a "movie" going on a screen the driver can see, but a LCD reversing camera / LCD mirror in new cars are okay to be on all the time, but of course this only display what is behind you.
With my old 4 channel analog setup connected to my 7" head unit in the car, i did try to drive by the LCD screen footage as it had no delay, but this is extremely dangerous and not something a sane person should ever attempt.
but just like flying FPV planes or quadcopters it can be done once you adjusted to the more or less skewed depth and distance perception the lens give you, and your eyes seeing the exactly same thing so they cant do the compensation they do when we see stuff.