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Do EEVEE samples really matter when rendering?

Can't really see a difference except for render time

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There are several things affected by EEVEE sampling, as you can see in this example scene, rendered at 1, 8 and 64 samples:

enter image description here

  1. soft shadows are obtained by sampling large light sources using many small light sources. Low samples will "reveal" the point lights. This is generally the main downside of a low-sample rendering, therefore you should choose the number of samples based on how good your soft shadows look.

    enter image description here top view: enter image description here

  2. the direction of refracted and reflected is also sampled because, especially around the corners, a sub-pixel change in the direction of the ray can make a difference between hitting an object, another object, or the sky. For low samples, this results in a strange pixelated blur

    enter image description here

  3. aliasing is what happens when a curved profile is drawn using pixels: it gets jagged if the pixels aren't "smoothed" (antialiased) adequately. More samples make the contours smoother.

    enter image description here

  4. [Added Sept 2020] the quality of Alpha Hashed transparency is also affected by the global sampling. Indeed, for each sample, a pixel will either be rendered as fully opaque or fully transparent: a fractional transparency is a result of averaging over multiple samples. With too few samples, tranparency appears patched/noisy:

    enter image description here

  5. [Added Sept 2020, suggested by Andrey Sokolov] the number of volumetric slices rendered depends on the EEVEE sampling: note how at 1 sample the dust cloud appears 2-dimensional.

    PS There is another "Samples" count inside the Volumetric tab that controls the quality of each slice, and is independent of the global EEVEE sampling.

    enter image description here

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  • $\begingroup$ Thanks! That's great $\endgroup$
    – four two
    Jan 8 '20 at 17:37
  • $\begingroup$ + Volumetric materials are also highly affected by render samples $\endgroup$ Sep 17 '20 at 8:12
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    $\begingroup$ @AndreySokolov yes, I mention that at the end of my answer. Volumetrics have their own sample count though. $\endgroup$
    – Nicola Sap
    Sep 17 '20 at 9:12
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    $\begingroup$ Sorry, I've missed it. Anyway, render samples and volumetric samples affect each other. Volumetric samples determine how many volume slices will be drawn while render samples determine the quality of each one. And the same is with motion blur: motion blur steps (in 2.9) determine how many subframes will be rendered and mixed into a frame while render samples determines quality of each subframe (divided by subframes count). $\endgroup$ Sep 17 '20 at 20:55
  • $\begingroup$ Oh I see, I haven't explored the interplay between the two sample counts, but your explanation makes sense. I'll see if I can demo it easily and add to the answer. Thanks $\endgroup$
    – Nicola Sap
    Sep 18 '20 at 12:17

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