Although it mostly signals that the Harvard graduate was a high school superstar and did not have parent financial (or other) limits against attending. But, if you were in a position to hire, would you judge college graduate applicants by their high school achievements?
It may be more like the minimum rigor of Harvard is not so much higher than that of a typical university, so that the students who can pass the admission gate do not find it that hard (unless they specifically seek out added rigor that is offered).