One of the reasons vitals are such a good diagnostic tool is that we monitor them specifically when we already suspect something might be wrong. Monitoring healthy patients reveals the large variation in vitals -- some that might even appear problematic.
We know this among other things because we have accidentally experimented on babies and mothers during delivery. Some clinics have a policy to put them on continuous monitoring the moment they arrive and they get treated for more things with worse outcomes when they're otherwise healthy. Maybe this is confounded (some clinics overmedicalise everything -- both monitoring and treatment) but I like the intuitive explanation that excess monitoring causes excess treatment.