We turn on our 4 way flashers partly because most of the trucks don't show there brake lights when only the engine brake is on, which is a good way to gradually slow down, save your real brakes for when you need them ...
Something not mentioned, but equally annoying is the idiot who sticks to the middle lane when there are three or more lanes ... I'm in the right lane, wanting to pass the slow poke in front of me, I have my left turn signal that activates SIX (6!) Blinking/flashing lights on the left side of my truck and trailer ... Yet idiot in the middle lane won't pull out into the far left* lane, even though there is nobody there!
*Us truck drivers call that "The hammer lane" or "#1 lane" ... In the above scenario the middle lane is #2, the far right is #3 ... And so on ... Far right is also called "The granny lane!"