Krodal:
If a pin is INPUT, the impedance is very high. So the pin is floating.
It is only floating if you don't connect it to anything and have it set LOW.
And who reads a disconnected INPUT except someone looking for randoms in a weird way?
You can connect a pin to ground through a switch, set the pin to INPUT and digitalWrite it HIGH then when you close the switch it will ground to LOW through the pullup resistor. That makes a nice, safe button/switch circuit which at no time is floating but does need to be debounced.