From Xojo Documentation
Called when iOS reports a low-memory situation. Apps should attempt to free up objects and other resources when this event is raised. If the low-memory situation persists, iOS may kill your app.
Your implementation of this method should free up as much memory as possible by purging cached data objects that can be recreated (or reloaded from disk) later. It is strongly recommended that you implement this method. If your app does not release enough memory during low-memory conditions, the system may terminate it outright.