I have mixed feeling about them. I too think they're kinda degrading, and insisted to my wife that we would never use one. Guess what? We got one as a gift.
My daughter, we never needed it for. She was always content to sit in the stroller or walk near us.
My son? Yeah, we've actually used it on him. Because he's like a goddamn greyhound otherwise. As soon as he gets loose, he's off and toddling. And if you're taking them somewhere like an open-air market where there's a lot of people and not necessarily enough room to cart around a ginormous stroller, then this isn't a terrible option.
However, I will ALSO say that its just so the parent can do whatever they want instead of, you know, actually paying attention to their child.
Spoken like a person who doesn't have a child. In order to go about daily necessities such as shopping for groceries, going to doctor's appointments, etc. it is necessary at times for a parent to devote less than 100% of their total attention to their child. If you have two kids, it's less than 50% each. And that few seconds' distraction is all that's needed for disaster to strike. The other day, I bent down to help my daughter get her shoes on. In that few seconds, my son raced down the hall and stuck his hands in the toilet. Why? WHO THE FUCK KNOWS?? He's 1, for god's sake! Kids *do* shit like that.
My point is, yes I don't like the visual analogy to treating my child like a pet. But I wouldn't use it much past the age where they'd actually be cognizant of that and where that would actually be a bad thing. For the next year or two, he'll probably think it's awesome that he gets to be like a dog. And we use it rarely, only it situations where it's outdoors and there's a lot of people and it's not a good environment for a stroller.