Hi high-spite,
Thanks for the feedback. Like with textures, where the suggestion is to have, at least, 1.5 times the resolution, to not noticeably lower the quality if the render (the 1.5 here means if the camera comes close, that this ratio is given, as it is nearly impossible with shaped objects to match each pixel from texture to render. Similar to that is the size of an object, since we have a very small one, typically with Particles. Here, the particle has a shape, which needs to "translated into the final pixel raster.
Like with any pixel movement that deviates from the next pixel position, changes that are longer or shorter will lower the quality. Lens distortion correction is a type of movement that affects quality.
The post effects can only "see" the scene through the rendering (the raster of the resolution), without any knowledge of the actual scene.
The Nyquist Frequency is a good way to explain it. Living in a cave and emerging only every 24 hours will give the impression that it is always night (or day, etc.).
Another point is that objects, especially particles, move, plus the camera might add screen movement for them as well. So they move through that raster of the final image. A typical example is Analog audio sampled into digital, which can lead to many problems if the resolution is not high enough.
But I get carried away here. I think the idea is clear, and I apologize for going on about it, but perhaps a few readers might find this supportive to know.
Cheers