Yeh it’s meant to be hazard warning. I try to make sure I use it for that purpose instead of an anger indicator. You should brake or do whatever maneuvers are necessary to avoid an accident as priority before thinking about the horn. That said it is useful to do in many of the same situations where the brakes ought also be applied. This is because you simultaneously want to avoid danger caused by the other driver through your braking while also getting them to realise that they’re causing danger and stop it. Hopefully both of those things will happen.