As you can see, Page Life Expectancy (PLE) on this graph dips, gradually climbs, and then dips again. With a collection every five minutes you may not catch the exact peak – all you know is that the PLE was 50,000 at 12:55am and then only 100 at 1:00am on 03/13. It may have climbed higher than that before it dipped, but by 1:00am it had dipped down to around 100 (coincidentally at 1am the CheckDB job had kicked off on a large database).
If you really need to know (in this example) exactly how high PLE gets before it dips, or exactly how low it dips, or at what specific time it valleys or dips, you need to actively watch or set up a collector with a more frequent collection. You will find that in most cases this absolute value isn’t important – it is sufficient to know that a certain item peaks/valleys in a certain five minute interval, or that during a certain five minute interval (“The server was slow last night at 3am”) a value was in an acceptable/unacceptable range.
Andy also gives us a set of counters he uses by default and how to set up automated counter collection. Left to the reader is integrating that into an administrator’s workflow.