on new cars if you brake hard the hazards will automatically go on as soon as the esp system kicks in, i disabled esp on my car but if i see a situation up front and i need to slow down in advance or brake hard the i switch my hazards on, also cape town is prone to some thick fog at times and due to the fact that 90% of drivers in cape town are aholes even with my fog lights on i will also have my hazards on as an additional warning.
rather safe than sorry
taxi's on the other hand just use hazards for fun, flashing lights amuzes them