It is bad to stay on FaceTime overnight as your phones battery may get depleted or you may not have enough bandwidth.
If you leave the FaceTime on overnight while sleeping then it will just waste your battery and data if you're on cellular data or have a limited amount of data to use.
However if you have the phone plugged in and have unlimited data then it's fine to leave the FaceTime on overnight but it's best to close it out if you're not awake and using it.
Using Facetime and charging your iPhone or other phone simultaneously is not hazardous for it.
In reality, many iPhone and android phone users do this, especially if they need to utilize Facetime for an extended amount of time.
It's crucial to remember that using your iPhone or android for a long time while it's charging can cause some heat.
One common reason why FaceTime calls may fail overnight is the lack of sufficient bandwidth during peak hours.
When many users are simultaneously utilizing the internet, it can strain the available bandwidth, resulting in poor call quality or dropped calls.