I am playing with Arduino and LEDs at the moment. LED needs a resistor to limit current, that's clear. However, all examples I see use separate resistor for each diode. As far as I can tell electrically (in terms of limiting current) it shouldn't matter much whether we use single resistor for all LEDs, or separate resistor for each one (see the picture). I already tried to discuss it with a friend of mine, and he told me it is better to use separate resistors, but TBH his explanation (different diodes may have different forward voltages, if they are connected through a single resistor they can have different brightness) wasn't convincing. So, is there a reason why we use multiple resistors?