data-konzept

'You often see Page Life Expectancy referred to as an interesting performance monitor counter. And it can be! It indicates for how long a page is expected to stay in cache, from the time it was brought into cache.

But just looking at a snapshot value doesn't say that much. It might be high, but that is because you haven't had a high turnover of you pages for the past couple of hours. Or the other way around, you happen to look just after a very rare monster query. Furthermore, having a log can show you how PLE changes over time. 

"The app was slow at two o'clock today."'...

http://sqlblog.com/blogs/tibor_karaszi/archive/2016/09/07/log-page-life-expectancy-over-time.aspx