The objective of Pry-Fi is to stop your information from leaking unnecessarily by completely deactivating your Internet connection. Once activated, it will stop your device from 'announcing' the WiFi networks it knows, without losing the possibility of connecting to known WiFi networks.
Pry-Fi is an app that's especially useful for users who connect to public WiFi networks. That said, your device needs to be rooted in order for the app to work correctly. If it's not, then you won't be able to use all the app's features.