I recently found some training information that discussed NOT teaching your dog a "LEAVE IT" cue.
This is particularly appealing because it results in your dog leaving things alone that are on the floor or ground.
I am not totally convinced yet though, that this is a good idea. Yes it is nice not to have to always be telling your dog to leave things alone and be always on the lookout for stuff he could pick up in his mouth.
However it also prevents, to an extent, your dog from interacting with the environment. If you dog was to not even sniff at things because he was trained to stay back or away from everything on the ground, that would be unfair to the dog. Dogs need to interact with the environment. They need to sniff.
This is why I teach my dogs a default leave it AND a "LEAVE IT" cue. I want them to sniff things on the ground when we are out for a walk but if there is too much sniffing in one place, I would use the "LEAVE IT" cue.