[cauch]

I agree with that.

It reminds me of the tomato. Some people don't know the tomato is a fruit. Some people know the tomato is a fruit and treat them like a fruit. Some people know the tomato is a fruit and still treat them like a vegetable because it is what makes sense.

In practice, I have never saw someone mistreating a badly written number in a way that had any impact. If they don't know themselves the concept of significant digit and believe the number is 1.234567890 precisely and not 1.234567889, what would be the wrong decision they will take that they would not have taken if the number was 1.234567889?

It starts to matter when you have 10% or ~100% uncertainty, in which case, writing 1.2 or 1 is still not enough to convey the meaning to someone who does not get significant numbers, because for them, 1 = 1.0000 anyway. In this case, you need to explicitly explain the limitation on decision due to the uncertainty.

In practice, splitting hairs on the significant digit convention is just missing the point: if you apply the convention to people who are not informed on the precision, they will make bad decision anyway even if technically the number has the correct significant number.