The LEDs quoted originally are Maplin
CJ69A. The specs say they draw about 8.5mA at full power. The extra resistor added to the circuit reduces that current draw.
I found if more than about 5 mA is drawn, the VIS motor got stuck in the activated/open position and wouldn't reset until I disconnected the indicators. However, I changed the circuit slightly using a separate resistor on each LED so that the LEDs light better. But it meant my circuit was drawing too much.
My point was just that there's no benefit in using higher brightness LEDs (e.g. @ 20mA each) as they won't be able to draw the current needed for that extra brightness.