oh yeah, site went down before I edited my post, was going to additionally ask do you mean actual sub pixels, and made these examples
<breakdown of a pixel on a TFT screen (full RGB would be white)
<theoretically utilizing sub pixels to move at finer than pixel amounts, only the top left, the bottom is at 3x zoom to breakup what is theoretically happening, to be honest it isn't very noticeable at all, and in pixel art and animation it's all about effective colour usage to imply the pixels are moving between each other.
*just read the thread response, I honestly think that 1bit sub pixel-less circle is as effective and smoother to my eyes, the one on the left just reads the same but with awful colour aliasing at the penumbra, helm's example is rather smooth and really fine amounts of motion is achieved within 2 pixel lines, also the only real practical use of sub-pixels on font is entirely scale relative and has a lot more going into it than simply using RBG values per pixel and is calculated and used as a form of anti aliasing
just zoom in on this to see exactly what I mean
if you had some fancy software you could turn a 1 bit animation at a higher resolution into a half resolution animation using sub-pixel anti-aliasing to effectively reproduce the same level of detail. but yes as everyone has said it's not what people mean at all when they say Sub pixel animation in relation to pixel art
*bit further away from my monitor, that circle slide does look smoother, but if it was greyscaled it'd arguably look as smooth