When turning the ignition to "ON" position, there is a slight sound that comes for about 3 seconds. My dad told me that it's a good practice to wait for some 3 seconds before cranking the engine. I'm sceptical about this and need some more information regarding the technical aspects in this matter.
P.S.: It's a petrol car. All info that I've found is for Diesel cars only. (Maybe I'm missing something?)
The slight sound you hear is probably the fuel pump coming up to pressure, so yes it's a good idea to wait.
If the car has been recently run < 20 minutes you may not need to, but if it has stood for longer then you probably should.
It depends on the car. Some cars pressurize the fuel system only when you turn the key, in which case it makes sense to wait a second or two for that to happen, otherwise your engine will just crank until pressure is achieved.
Many newer cars will pressurize the fuel system when the drivers side door is opened so by the time you are seated it's ready to go. If you have one of these there's no benefit to waiting.
