I once heard the saying that walking your dog without letting them sniff is like going sightseeing blindfolded. Can you imagine how boring that would be?
The world for a dog is largely made up of the smells that surround them, and being able to explore these offers your dog the chance to gain valuable information about their surroundings... the last squirrel that ran past, the last dog that stopped there or perhaps one that walked the same route two days before. Letting your dog sniff along the way offers a good form of mental stimulation and sensory enrichment, and offers your dog a sense of autonomy and control over their environment as they move through it.
All too often you'll see dogs being rushed along, hurried past every smell as they walk down the street in order to get to 'the walk'. If you give your dog the freedom to smell and stop as you go this part of the journey can be just as valuable and just as enjoyable for your dog. I appreciate that stopping every at every tree when you're in a hurry probably doesn't sound like an ideal dog walk, but compromising to allow this some of the time may result in a stronger bond between you and your dog and more attention during the key moments you want to move along faster. There is no reason you can't teach your dog to walk alongside you for part of a walk and have a longer lead or complete freedom to move from scent to scent during others.
I have been practising this with my own dogs recently, using a 'focus' or a 'with me' cue (I like to use 'with me') during the moments I'd like them to walk next to me and focus on moving along, and release cue (I like to say 'okay, go') once they can explore more freely so they know the time I'm asking for their attention has come to an end. Once I give this cue, I let them guide me as to how fast they want to move and where they want to stop. In order to cue 'with me', I began by clicking and treating each time they were walking by my side with a loose lead or looking at me during the walk (effectively as a heeling movement), and then paired the cue word as they began to do so more regularly. At the 'okay, go', when they were then free to move as they wished, I made sure to stop at the first sign they wanted to sniff, giving a longer lead and matching my pace with theirs. Whilst they still love their time in the park itself, I have noticed considerable more attention from them on our way there. Walking this way benefits them and gives you time to notice the little things you might have otherwise rushed past!