The Internet report that I saw gave various reasons to NOT blow your horn. Some of them are as follows:
1. The Japanese Road Traffic Law states that a vehicle horn should be used only in an emergency OR in a dangerous locations where there is a signpost.
2. a vehicle hron is often used to warn pedestrians that the car is approaching them from behind. Such horn use violates the law.
3. There is concern that the effects of a vehicle horn on people outside the vehicle including pedestrians and residents who are living in neighborhoods with narrow roads may be serious.
4. Long honks and horn use to gain another's attention or to alert another to dangers often aroused negative psychological reactions in listeners. These reactions were more remarkable for pedestrians.
5. Some people found horn use to be "startling", "noisy", or "irritating.
More good reasons to NOT blow your horn. I suspect (think) that it is also stressful to the HONKER as welll as the HONKEE.