No effect, but long charging is not recommended.
Because at present, most of the smart phones we use are lithium batteries, and basically have their own PMU module, a simple translation is the power management unit, one of the functions of this unit is to manage the power, and the current is also its pipe, it can be plugged in after the user, automatically to detect whether the current battery power needs to be charged.
The mobile phone also supports the fast charge function, which controls what time to fast charge and how long to enter the slow charge, preventing current overload and causing high temperature of the mobile phone.
After being fully charged, the PMU will also automatically give a power off signal to prevent the phone battery from continuing to charge and entering the standby state. If long charging does have an impact, mobile phone manufacturers will not invent wireless chargers, which are continuous charging.
Yes, today's mobile phone batteries do not charge overnight like in the past, which has no effect on the phone.