Why is it that we use voltages and watts more often than amperages? 9v batteries, 12v car battery, 1000W Microwave oven. But amperages not so much, even though its “half” of what makes power, A*V=W. What property of amperes makes it so “unnecessary” to be aware of?
Bonus: how many amps and volts does a typical 1000W microwave use?
For an example of where constant current sources are used – and IMO, deeply necessary – we can look to the humble LED driver circuit. LEDs are fickle devices, on account of their very sharp voltage-current curve, which also changes with operating temperature and is not always consistent from the factory. As a practical matter, the current through an LED is what predominantly controls the brightness, so constant current sources will provide very steady illumination. If instead an LED were driven with a constant voltage source, it would need to be exceedingly stable, since even a few tens of millivolts off can destroy some LEDs through over-current and/or over-heating.
For cheap appliances, some designs will use a simple resistor circuit to set the LED current, and this may be acceptable provided that the current is nowhere near overdriving the LED. Thing of small indicator LEDs that aren’t that bright anyway. Whereas for expensive industrial LED projectors, it would be foolish to not have an appropriately designed current source, among other protective features.