So for insurance if you are rear ended or something?
I was one car behind a pretty nasty accident.
Speeding sedan clipped a minivan during an aggressive lane change.
Minivan lost control hit the media and flipped, sedan just took off.
If I had the camera at that time I would have had a clean shot of his license plate.
Rear camera would also catch someone on their phone or not paying attention if they rear ended you.
Same with the sides, plus wiring in 4x isn't that much more work than one or two.
Side cameras give a wider field of view for relatively low cost upgrade.
Plus, some times, I just see some funny shit on the road and can't get my phone out to take a picture.