I find it extremely rude and arrogant.
It is to let the driver in front know that faster traffic is approaching
I'm scanning front, instruments, and mirrors. I don't need some wanker flashing his lights at me ... I already see him.
I spend 2.5 hours every workday traveling in moderately heavy traffic, on 4-lane divided highways, at speeds well in excess of the posted limits. I see a lot of cars, and a lot of drivers. I'd say about 99% of these drivers know how to get along ... the real hazards to the rest of us are not the left-lane slowpokes. Such creatures are almost nonexistent.
The real hazards are the headlight-flashing tailgaters and the lane-weavers.
These foul folk should be taken out and shot.
Agreed!
You are the one causing it so stop holding up traffic. Here in So.Cal I see you guys driving like little old ladies in the passing lane clinging to power as you control the lane making people pass you on the right while you stop traffic flow and cause dangerous lane changes.
It is a weird sight to see and I am amazed at how many of them are white males with both hands on the wheel looking straight ahead like they don't know what is going on around them, it is what I think of as passive aggressive behavior to make up for whatever inadequacies they feel in life, for those moments that they block traffic, they feel in control of events.