The reddit explanation in the post addresses your question I believe. If someone is at a 28 or 29 a few "charity" points can be found in subjectively-graded tests.

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jameshart 2 hours ago | parent | next [-]

I think that really just reflects the fact that on subjectively graded tests the score really doesn’t have that many significant figures of accuracy. That a regrading can find 3 to 5 points by being more generous - or presumably take 3 to 5 off by being harsher - says that really you could save a lot of effort by treating the final grades as bucketing into 10 point bands and treating 25-35 as the actual cutoff.

	▲	aesthesia 31 minutes ago \| parent [-]
		Isn't that equivalent to just setting the passing threshold to 25, with the same incentives?

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dvh 2 hours ago | parent | prev [-]

If you grade individual questions, you don't know the total score.

	▲	rvba 2 hours ago \| parent [-]
		The incentive to find the extra point would partially disappear.