great topic lol - I think it boils down to each hardware setup in all honesty.
I had no resistor or capacitor it all worked, i fitted both, it still works and i don't notice any difference, I only picked the capacitors up as i was getting other things from that place and they were cheap and i was curious more than anything else as WLED has it on their main diagram.
but im still on the if you have a decent psu that can put out the proper current and voltage required - it should be on tap to use, as and when the LEDS require it, whether the capacitor does provide the litlle burst at the right time - who knows but as most vids or tutorials use the barrel connectors as they plug into the brick psu im happy believing that you only need it if you have one of those unstable PSU's
Resistor on the 1st led to protect it - could be the case if your running slightly higher than 5v and your MCU is out putting 5v , resistor could pull that signal down to a more cleaner stable level but meh im quite happy to chop it off if needed and move the wiring down 1 led.
Just my thoughts on it