The data is saved in an XML file in the app's private folder, located at /data/data/pkg-name/shared_prefs/pkg-name.

You shouldn't use player prefs as a saving system, but it's perfect for storing player settings such as audio settings or graphics settings.

The Player Prefs class in Unity is used to save small amounts of data from your game to disk, which allows you to store and recall single string, integer and float values between gameplay sessions. This can be extremely useful for saving and loading basic sets of data, such as option settings or simplified game saves.

In case when the game crashes or otherwise prematuraly exits, you might want to write the PlayerPrefs at sensible 'checkpoints' in your game. This function will write to disk potentially causing a small hiccup, therefore it is not recommended to call during actual gameplay.” In other words it just only for security.