From the Uberguide and manufacturer specs we all know that:
It’s very strongly recommended that each NeoPixel have an accompanying 0.1 μF capacitor between +V and ground.
However it seemed to me that it might be possible to use one cap between every other pixel. And sure enough the Neopixel rings are designed this way, as noted in the Uberguide:
It’s occasionally sufficient to have one capacitor between pairs of pixels; some of our NeoPixel rings work that way.
So what determines the occasional case?