Quote from the 2.2.03.1 RC changelog:
Improvements to soft shadows:
- Soft shadows now use a slightly better sample distribution to slightly reduce noise.
- Sunlight has a new option "Sample jitter". Default value is 1 which qualitatively matches the old behaviour, giving jittered stratified sampling which is statistically unbiased but produces noise. A value of 0 produces no noise, but introduces bias and stepping artefacts instead. This may be favourable in some situations, e.g. animations.
- Soft shadows of Sunlight nodes no longer flicker between frames in an animation, provided that jitter is set to 0.Quote from: Oshyan
I think the sample points would still vary *between frames*. The better approach, as with atmosphere, is just to use sufficient sample levels to avoid noise and thus the "flicker" (which is really noise variation between frames) won't occur.
- Oshyan
The jitter creates the variation between frames
For every frame the jitter creates a different sample pattern and that's why you need more samples, in order to have the result converge with previous/next frames. Without jittering the sampling is more evenly distributed, but can create bias/stepping as you can see in the quote above.
You are right though that with atmosphere it's better to use jittered sampling and increase samples, as reduced jitter can result in artefacts as Richard has just shown and is also in the quote above.