[TeeJay942]

I think FB focuses it's business around increasing time in app per user (or they at least track this). Many to-do list apps track tasks completed.

I would say for any completely free games that do well b/c they advertise, optimizing for time in app and # of clicks on ads is clearly very important metrics.

I built an app that helps you build habits by scheduling them into your daily morning/evening routines. Part of that routine building process is assigning time for each action (e.g. exercise for 30 minutes). So my KPI is minutes completed.

It's a productivity app so it seemed foolish to me to try to keep people in my app for longer. I even encourage users to complete their routines through actionable notifications (i.e. without opening the app).