Both are in adafruits best practices for neopixels/WS2812b
They go on to bold a section stressing the importance.
- Any project with a lot pixels or a large power source should definitely include the power capacitor and data line resistor.
and even give a big red bold warning on the "Powering Neopixels" section
- Adding a 300 to 500 Ohm resistor between your microcontroller's data pin and the data input on the first NeoPixel can help prevent voltage spikes that might otherwise damage your first pixel. Please add one between your micro and NeoPixels!
as well as give some information about why you should use caps
- Before connecting a NeoPixel strip to ANY source of power, we very strongly recommend adding a large capacitor (1000 µF, 6.3V or higher) across the + and – terminals. This prevents the initial onrush of current from damaging the pixels.
Edit: It's really easy to add both so I've never questioned it. They may not make a night and day difference, but they certainly don't hurt anything. And as the old adage goes, better safe than sorry.