The book Superforecasting documented that for their best forecasters, rounding off that last percent would reliably reduce Brier scores.
Whether rationalists who are publicly commenting actually achieve that level of reliability is an open question. But that humans can be reliable enough in the real world that the last percentage matters, has been demonstrated.
It seems that you reversed your point then. You said before:
Even before I read your comment I thought that 5% precision is useful but 1% precision is a silly turn-off, unless that 1% is near the 0% or 100% boundary.
However what I am saying is that there is real data, involving real predictions, by real people, that demonstrates that there is a measurable statistical loss of accuracy in their predictions if you round off those percentages.
This doesn't mean that any individual prediction is accurate to that percent. But it happens often enough that the last percent really does contain real value.
Whether rationalists who are publicly commenting actually achieve that level of reliability is an open question. But that humans can be reliable enough in the real world that the last percentage matters, has been demonstrated.