When running on cruise in the left lane on the #2 or Yellowhead, (in daylight hours) I routinely use the "flash" function of my high beams to alert others that I am travelling faster, and would prefer to not overtake them on the right.
In a perfect world, everyone would be diligent when it comes to the matter of "spatial awareness", but sadly, this is not the case.
This is exactly why automakers provide this feature in vehicles.
At night, I am much more "discerning" when it comes to using this feature and will never "flash" someone at close range; usually I just signal and pass on the right, if safe to do so.
As a side note...I wish a few more people would figure out the fact that you can use your accelerator pedal, without having to reset your cruise control. Those folks that sit in the left lane overtaking a semi at 2-3 km/h...I'm talking to you.
I would love to see how some of these "folks" would "cope" on the busier Interstates in the US. "Flashing" is common (in my experience) and no one seems to take any great offense down there...here?