When to shown app intro onboarding? before or after sign up

For mobile applications when it is good to show the app intro onboarding(slider with app features). I have seen some mobile apps showing app intro before signup process and most after. Which is most effective?

According to my view, if a user install app directly after browsing app store, its better to have upfront app intro, since user may not have read the details about the app (installed at the first glance). For user who read about app somewhere and installed it is better to have app intro afterwards, since user already know good deal about the app. But that's my view, it's not users. Most of the time, I skip the app intros, since I just want to get to the main screen of the app.