I used to charge my phone overnight all the time. Since I used to use some sleep sounds on my wireless earphones, it was perfect.
Finally after replacing one battery and having another one on it's way out, I think I believe this. You shouldn't charge your phone overnight.
Some tech experts at ZDnet are saying you shouldn't do that, primarily because it heats up your phone and is bad for the battery. Sure your phone has smart charging capabilities but the phone is still plugged in and the best thing to do is charge a little bit at a time.
So when you wake up they recommend a charge of 30-45 minutes and then charge it in the mid afternoon to get it to 80%. The idea is to have your phone charging for less than 2 hours a day.
More on battery health and charging your phone here.
Photo credit: Kinga Krzeminska Moment