Yeah, this is the usual consideration, but have you ever actually tried using just 1 series R
for multiple Leds? I'm just curious as to the actual results.
If the LEDs are of different colour then only the colour with the lower voltage will come on. Beginners often try and use RGB LEDs with only one resistor.
If the LEDs are of the same colour then they will not share the current equally and one will be brighter than the other. Maybe if running at more than half the maximum current one LED will have too much current and burn out a lot quicker.
If the LEDs are being controlled separately but still have one resistor. Then the brightness will depend on how many LEDs are turned on. This is what happens when beginners put one current limiting resistor on a seven segment display.