Comparisons of these two nearly always list what each does well, which is the less useful half. What a site has to plan around is what each one structurally cannot see, because those gaps are where the failures that surprise people actually come from. Both have a blind spot, both blind spots are permanent rather than fixable by doing the same thing harder, and knowing where they are tells you what else has to be in place around whichever strategy you have chosen for a given asset.
What preventive misses: everything between visits
An interval catches wear that accumulates on a schedule. It cannot see a fault that develops in the eleven weeks between quarterly visits, and shortening the interval to catch it is expensive and only partly effective. That gap is exactly the space predictive monitoring occupies, and it is why monitoring is worth the step cost on assets where a between-visit failure is expensive.
What predictive misses: everything nobody measures
Monitoring sees the failure modes its instruments are aimed at. Vibration analysis says nothing about a corroding drain pan, a blocked condensate line, a seized damper or a filter nobody changed. On a monitored asset it is entirely possible for the monitoring to be green while the unit fails for a reason no sensor was watching, and that is not an implementation flaw, it is the shape of the strategy.
What neither one sees: the asset that is not on the list
The largest gap at most sites belongs to neither strategy. It is the unit nobody knew about: the split serving a comms room, the pump in a basement, the item that arrived with a project and never reached the asset register. No interval and no sensor covers an asset nobody has recorded, and walking the site against the list finds more risk than most changes of strategy.
Questions people ask about preventive maintenance vs predictive maintenance
Does running both close every gap?
It closes the two strategic ones on the assets where both are applied. It does nothing about assets missing from the register, which is why the register is the first thing worth auditing.
How do we find the failure modes we are not covering?
From your own failure history: every failure on an asset that was on a plan is direct evidence that the interval or the checklist missed something. Each one deserves a specific look rather than becoming a statistic.
Is inspection a third strategy?
Inspection is usually part of a preventive visit rather than a strategy of its own, and where it is doing the real work it is worth naming so that its interval is chosen deliberately.