It’s important to your dog’s physical and mental well-being that you give them lots of opportunities to sniff on your walks
Not only do dogs have hundreds of millions of scent receptors but they also devote 40 times more brain volume to decoding smells than we do. A dog’s sense of smell can loosely be compared to human sight. Actually 1/8 of the dog brain is dedicated to interpreting odor which is even larger than the section of our brain dedicated to interpreting sight.
Many pet parents make the assumption that a faster, longer walk will tire their dog out more. However, the mental stimulation a dog receives from sniffing is much greater. This means a shorter walk with more sniffing can tire them out and they will generally be more relaxed and less likely to exhibit destructive behaviors at home.
A dog’s natural sniffing behavior is calming and has even been proven to reduce their heart rate.
Sniffing is also an important part of dog communication. Coming across scents from other dogs can tell them if that dog was male or female and whether they are in the vicinity or not. Sniffing is how dogs learn about each other.
Sniffing the environment is part of your dog’s experience of the world, we should give our pets space to be their natural selves embracing their instincts. 
While making sure your dog gets adequate exercise is important, it is also essential to make sure they have time to sniff and learn about the world around them
Fun Fact: The vomeronasal organ, also known as Jacobson’s organ, is responsible for the odd dog behavior of licking other dogs’ urine. Your dog is using their sense of smell to learn more from that pee than we’ll ever learn from a handshake.