This greatly depends on a number of factors, such as what parties are involved and which of your data they have obtained. Companies such as Google and Facebook, for instance, use information related to your preferences and search queries to show you advertisements they think you’ll be interested in. On the other hand, cybercriminals can very easily obtain your bank details to enrich themselves with your hard-earned cash, if you fill out your login info on an unsafe public WiFi network. These are just a few of the reasons why we always recommend taking several precautions online, such as using a VPN.