It's also psychologically harmful to have the positive test hanging over your head. I'm nearing the age where doctors start harassing about colonoscopies. You can do an at-home test instead of the full procedure, and it has a very good chance of ruling out the need for a colonoscopy. But it also has a high false positive rate; there's a decent chance that you'll end up in a state of "need a colonoscopy, also a colon cancer screener flagged you". I'm dreading the colonoscopy prep, but I'm not doing the at-home thing.