You second paragraph is wrong. SNPs are interesting because they exist in a significant part of the population. But a new mutation never reported before can as

You second paragraph is wrong. SNPs are interesting because they exist in a significant part of the population. But a new mutation never reported before can as dangerous as you want. A case we found: a woman already developed an illness in her adult life, lets supose it was renal failure. We suspected a genetic root, so we sequenced her exome, founding a never reported mutation that frameshifted a gene previously associated with renal failures. We quickly panel-sequenced her parents and children to check if they had the mutation, which none of them had. So the woman had a de novo mutation in heterozygosis that their little kids were lucky enough to avoid. Imagine the relief. Not useful? I disagree.