I use it, only when I have to. I'm not a New York taxi driver...but it does get used.
There's an escalating trend in The Midlands, UK of jumping the traffic lights, or 'running a red light' and there are certain members of the community, that will even follow drivers running a red light.
Truck drivers on the motorway, in stationary traffic, will pull over to restrict your progress, as will car drivers in the towns, during heavy traffic/rush hour.
Everyone, it seems, will text, or make a phone call and drift across your path.
I need a louder horn, than the OEM.
Yeah I very rarely (basically never) use mine but if I ever do need one I want it to go off like a nuke, not a whoopee cushion. Plus, it's nice to know you don't have a crap horn on the bike but something that will do the job.