The effect may be comical, but it has a more serious purpose: it ensures that I can be seen by the morons that infest the roads of our noble capital city. Whereas the front light on the handlebars is - obviously - constrained to shine in the direction of travel of the bicycle, the light on my helmet shines in the direction I am looking. Thus, if you are the driver of a car, waiting at a junction and about to pull out in front of me and where I have the right of way and you do not, I merely have to look at you and you will have a flashing light directed straight at your face.
This makes it very difficult for you NOT to see me.
Consequently, if you do pull across me and cause me to skid, leave my bicycle at speed and hit the road, I will be able to justify my claim that such an occurence will be entirely due to negligence on your part. I will take the line that you have caused an accident and I will want to involve your insurance company in the matter. If it transpires that you do not have insurance, or if you do not wish to furnish me with details, I will take your VRM and I will involve the police.
In short, I will sue.
That is all.