http://o54hon2e2vj6c7m3aqqu6uyece65by3vgoxxhlqlsvkmacw6a7m7kiad.onion/en/blog/2019/6/28/secure-wifi-happy-lifi
To put it briefly (and really skip at least 71 hops): when you use a device, that doesn't use strong encryption, to send any data through the Internet, from point Wi (device) to Fi (website), it is entirely exposed. It will be open for a cyber attacker to get in between these transmissions. Some might read, steal and even use that information against you.