For me its -1
(+1 - Because yes, its very annoying when someone spam the horn without real reason.)
-1 - Because (I talking about only EU2 Calais-Duisburg road) sometimes I "have to" spam the horn too, when someone going with 40-50-60 km/h on CD road and block the traffic with this speed, of course because this "someone" there are always lot of crashes, because every player who want to drive faster on this road, try to overtake the low speed guy(s) and they make accidents.
Thats why I spam horn on these low speed guys,
1. because they make big traffic jams with the low speed;
2. because they driving low speed and blocking others, other players trying to overtake them and make crashes.
And I think if they make crashes, not their fault. The low speed players fault. If these people want to drive slow, or follow the speed limit, than go and drive at an other region or server (EU1).