The connection to the Warrens makes 'The Conjuring 3' a movie based off a true story. Ed and Lorraine Warren were paranormal investigators who documented many strange happenings. Their case files are full of accounts of haunted houses, demonic possessions, and other spooky stuff. The movie takes these real - life accounts and adapts them. It might not be a completely accurate retelling, but it uses the real - life basis of the Warrens' investigations to create a horror story that has some truth to it. Their real - life work provides the framework for the movie's plot, from the types of entities they claimed to have encountered to the methods they used to deal with the paranormal.
Well, it's based on the real - life work of Ed and Lorraine Warren. They were renowned for their paranormal investigations. In 'The Conjuring 3', the movie draws on their experiences. For instance, they might have encountered a particular type of haunting or a possessed individual in real life, and that gets translated into the movie's plot. So, their real - life cases are what make this movie based on a true story.
The fact that it's based on the cases of the Warrens. They were real people who investigated paranormal stuff.