TASK: Go into to your phone, laptop and computer and look at the history of the Wi-Fi networks you have connected to in the past year. They provide a history of where you have been. Some are obvious, like 'Hotel Y' or a certain gym or airport. Others that are not obvious are still known to providers and databases that collect the location of Wi-Fi routers. Most people's home Wi-Fi networks are known in terms of location. So as part of your general phone cleanup process try and remember to delete the Wi-Fi networks you no longer use.
WHY: This is just another way to track where you have connected to in the past. This provides valuable information about your location over time.