It all depends. There’s no set rule.
It depends on the price of the dropped food,
the wetness/stickiness of the dropped food,
whether someone is watching,
and the reflexes of the dog in the room.
If there’s a cat in the house, dropped food goes in the trash, every time.
You got a problem with cats? My cats are fastidious. They clean themselves very well every time they use the litter box. Then they jump up on my desk and lick me in the face, just to make sure their environment is clean. Or maybe that's how they clean their tongues?