Would have saved us from all the people who reject any sort of optimization work because for them it is always "too early" since some product team wanted their new feature in production yesterday, and users waiting 5 seconds for a page load isn't considered bad enough just yet.
It means "We think we have something that could help performance based on a dubiously applicable idea, but we have no real workload to measure it on. But we're going to do it anyway."
So it doesn't save us from anything, it potentially delays launching and gives us the same result that product team would have given us, but more expensive.
the problem is that it doesn't say that directly so people without experience take it at face value.
There's only so much you can do with people who will not even take the complete original sentence, let alone the context. (That said, "premature optimisation is the root of all evil" is much snappier so I do see why it's ended up being quoted in isolation)