A lot of people have asked me if sniffing on the walk is a good idea or not. The answer is not as simple as a definitive "Yes" or "No". Please allow me to explain.
When a dog is sniffing obsessively, the nose is tied to 70% of the brain and the dog is in “hunting mode”.
“Follow mode” requires a dog to stay next to or behind the human while “hunting mode” is all about tracking the scent and charging after the prey ahead of the human.
Therefore, it can be rather confrontational to get a dog to walk next to us attentively (i.e. trying to put the dog in "follow mode") when the dog is sniffing obsessively (i.e. the dog is actually in "hunting mode").
On the other hand, once the dog wants to follow the human organically (i.e. the dog is already in "follow" mode), everything will make much more sense to the dog without constant conflicts. That is why when we try to teach a dog to walk on a loose leash, we will always work on getting the nose off the ground first.
Does that mean the dog can never sniff during a walk? No.
We put sniffing on cue so the dog is released to sniff when we want him to (e.g. when we come across a patch of grass for the dog to potty on, when we are doing a tracking exercise, when we just want the dog to be free and enjoy himself, etc.). But we also teach the dog to get his nose off the ground and follow us once we ask him to.
A dog’s behaviour is rooted in his default decision making process. This process is about where his priorities are. Nurturing “follow mode” this way will help to set his priorities straight so he will prioritize following his human rather than going after whatever he wants whenever he wants to.
That is why we teach the dog to walk next to us without constant sniffing (i.e. in "follow" mode as default) and only sniff when we give the dog an invitation to do so (i.e. put "hunting" mode on cue).
Hope this makes sense.