Denny Cherry shares a few thoughts on Page Life Expectancy:
One of the very misunderstood values that you can monitor in Microsoft SQL Server is Page Life Expectancy (PLE). I’ve read online that many people think that the value of Page Life Expectancy is worthless to monitor. And that really isn’t true. While Page Life Expectancy won’t tell you a specific problem by itself, it can be used to point you in the correct direction so that you know where to look.
There was a backlash against PLE, specifically the “PLE should be at least 300” concept, but Denny throws that away and digs into the actual benefit from observing this metric.