If you are at a public WIFI and you are visiting a secure site using https or ftps for example your data is encrypted. anyway. if you visit an insecure site using http or ftp for example your data is not encrypted.
Using a VPN does not secure your data, If you are using a public VPN then navigating to an insecure site such as an http site then at some point your data leaves the VPN to connect to the insecure destination, so your data is no longer secure just as though you never used the VPN.
So unless you are connecting to a corporate network or by-passing country restrictions then the VPN is doing you no good. The real value of a VPN is when connecting point to point so that your computer becomes a node on the remote network. So if you are at a coffee shop or other public WIFI and you are using a VPN tpo connect to your corporate office network then a VPN makes sense and should be used. If you are at a coffee shop or using a public WIFI and you are connecting to a secure site then your data is encrypted and secure even when not using a VPN.