People are often confused about what's 'right' in walking their dog. Many believe that their dog should be firmly glued to their leg throughout the walk and just as many feel that their dog should have maximum freedom - both have benefits but both also have issues.
A dog who has to stay next to their person for the entire walk is being deprived of the main purpose of walking a dog which is (ideally) to explore their environment and keep themselves 'in the loop' with the neighbourhood. A dog's ability to sniff when on walks allows them to 'read the newspaper' of their doggy world. However when a dog is allowed to roam freely on walks (or sniff at will when on leash) we often get pulling on the leash, entanglement as our dog winds around us time and again and even those painfully slow walks where we may be lucky to cover 5 metres in as many minutes! Yes, that dog is well-versed in the news of the neighbourhood but will also be far lass responsive to any requests by his or her person.
From our perspective as both dog trainers and dog behaviour consultants we like to strike a balance. There are times that we NEED our dogs to walk next to us; crossing roads, negotiating busy footpaths and other pedestrians, and sometimes even to pass dogs who it may not be appropriate to engage with! Once we've successfully negotiated those things, however, we will ideally 'release' our dogs - not letting go of the leash, necessarily but giving them permission to have more space and to now read their doggy newspaper. As a general rule we encourage our people to only ask their dogs to 'Heel' for short bursts - as a rough guide we say 30 seconds at a time as this is generally the maximum amount of time that a person to be able to motivate their dog (and also enough time to get past any situation they may be faced with).
Since spending the entire time walking at our dog's sniffing speed isn't necessarily working for us we also need to set a limit on that side of things. If your dog has a 180cm leash, for example, we can reasonably allow them to cast that distance ahead of us, find something to sniff but be ready to move off with us by the time that we have passed them and are now 180 cm (the length of the leash) ahead of them. Dog gets to sniff, person gets to walk and all is good in the world! :-)