"Views" tells you how many times any user has viewed your app. "Users" tells you how many unique users have viewed your app. "Sessions" tells you how many times a unique user has viewed your app without leaving within a time frame. When we created the Executive Report, we felt "Sessions" was too complicated to understand and doesn't always get reported in the same way. For instance, some analytics tools define a session as "unique users who viewed your app within 5 minutes". Other analytics tools might define a session as 10 minutes. This is arbitrary and hard to explain. 

If you're trying to measure total engagement of your app, we would suggest using "Views". If you want to measure total reach of your app, we would suggest using "Users".