I didn't use a leash, however one of my kids was a real bolter as a toddler. She just didn't stay close and even when she was close her attention would get drawn to something and she'd be off without a word, and fast! I thought about getting a leash for her, and might have if my older child weren't old enough that I didn't have to worry about both of them - and in fact helped me keep track of her.
On the other hand, this child was probably 3, but maybe 4, and was in a play area and was held back from the play due to the leash. I wonder if that's a bit old for leashes, and if about using them inside a safe area (ie without traffic.)
Have you ever used them? Have you ever thought about them? Do you have an opinion on them? AND, do you (like me) think they are reasonable in some cases but question them in others (like for kids a bit older than typical, or in a safe play zone.)
And then on the other hand yet again, it occurred to me that this child might have had special needs that had the parent worried about him wandering off. I didn't notice anything about him that would lead me to think that, but of course I'm not his parent and don't know what's up. I am wondering about them more in general than about this particular mother. I do try to reserve judgement about specifics because I don't know what all is involved, but seeing it did make me wonder in a more general sense about leashes in safe places like that.