Default digital/analog pin state - input or output? (do unused pins need to be grounded to prevent floating inputs)

Projects Programming
11

IMO; recommend define electrical potential (a.k.a. level) of all unused pins.
I also do that for all my projects.

Floating unused inputs of CMOS ICs (not Arduino) with built-in protection diodes is not allowed many cases in this forum, but allowed floating unused inputs of microcontrollers with built-in protection diodes.
I thought there is mysterious tendency.

EDIT:
This is not the case for uCs that can turn off the any pin's digital input buffer.
ATmega328P does this only for PORTC (has Analog function).