"Leave It" Cue
Dogs will eat anything! They are faster than us, too. Leave It can save their life if you drop your medicine on the floor or spill a box of chocolates. It is also useful for cats, other dogs, squirrels, people on bicycles or skateboards, etc.
Using "Leave It" for safety
The "Leave it" cue is not just a fun trick to show your friends. Dogs will for-real eat just about anything. They are like toddlers who put everything in their mouths! The goal of the "Leave It" cue is to tell your dog to remove all focus on whatever it is they are starting to focus on. "Fuggitaboutit!"
If we put a treat on the ground in front of our dogs, tell them to "Leave It", wait a few beats and then say "OK", you can have it... will they 'fuggitaboutit'? Not likely. They will stare at it, anticipation building, until you give them permission to pounce. That is not what we want when the thing you're telling them to leave could kill them, or they could kill it.