Pros: Retractable leashes are great for not having to worry about handling excess leash and gives your dog more freedom with only one leash.  They can be used as a one-leash-fits-most system for a variety of applications; detection, tracking, running, etc.  Though most old-school trainers frown on the "new" technology, retractables rightfully have their place.  For pet owners, I recommend one retractable leash and one 5-6' regular leash to cover all your needs.   

Cons: The largest con, from the perspective of good trainers, is that handlers won't know how to properly use them when doing delicate tasks like detection or tracking where leash skills are top priority.  Meaning, handlers will push the button at the wrong time to stop the leash and in turn unknowingly give the dog a slight correction.  I also would not recommend these for obedience or giving corrections. ​

"I own a few retractable leashes and love them.  I hang them by my exit doors at home to take dogs for a walk or move dogs around the property.  I've also found them to be great for potty training and going on runs.    ​However, I personally have not made the switch to retractable leashes while doing police K-9 work; I've stayed with biothane and leather.  On the contrary, I've done a few felony tracks through corn fields and heavily wooded areas where I would have gave anything to have a retractable leash for officer safety.  Every time that 30' tracking lead (non-retractable) gets wrapped around  a few corn stalks or a small tree, those 5 seconds to unwrap it, are 5 seconds my eyes were looking down. In police K-9, we need to think about having a retractable leash to switch to or choose during those extra dangerous situations in heavy terrain."   -Matt Cox, Impact Dogs owner  ​