Round here, some people hit the horn at blind bends but that assumes that the oncoming driver (if there is one) had heard the noise - if they can hear at all. Better, IMHO, to respect the road and the conditions.
My sister totalled her Juke (it improved the looks) in a head on collision on a single track blind corner which goes under a railway bridge/embankment not far from her home. In daylight.
She sounded her horn. As soon as her horn sounding ceased she heard the horn of another vehicle coming the other way.
Since each driver, like all locals there, habitually sound their horn at this point, almost unthinkingly, without slowing down sufficiently, nor expecting an oncoming vehicle to be there, and, frankly, were tooting in the standard Mr Toad "I'm coming through! Beware! Get out of my way!" fashion, an expensive shunt occurred. The village fallout of which has still not been resolved a few years later.
I've been forced to bail twice by oncoming in the same place whilst cycling. NO horn the driver can here to respond with, and they are, of course, comin' thru! But my all time fave was the nobber who tried to overtake me as I approached the bridge.
Better, imo, for drivers to just chillax and to slow the feck down. But that will never catch on.