In many countries—not just Russia—dashcams have provided crucial evidence to vindicate people involved in accidents and tickets. A video showing that the light was yellow or that the accident was not, in fact, your fault, can mean the difference between keeping and losing a substantial sum of money. Porting this idea over to bikes, the Fly6 combines a small camera into a bright tail light and can be a pivotal witness.
See here. The above video shows a cyclist being groped by a dude on a motorcycle—something which he otherwise wouldn't have been able to prove. On the Fly6 website there are dozens of other examples of accidents, traffic tickets, and other incidents where video proved decisive. The rear-facing camera may not capture everything, but it's definitely better than nothing. For even the causal biker, why wouldn't this be a riding essential?