tea_love wrote:not sure if there are other reasons, to me it is dangerous when it doesnt hold the lid. Once I poured hot water over my pot and the leash was loosen and didnt hold the lid when I poured. I was lucky because the drop didnt break my lid. From that moment I decided to cut the leash and try to be careful when pouring.
One problem is that the lid can swing and hit the pot itself, depending on the length of the cord. Also, the cord can make it hard to rest the lid somewhere safe, leading you to have to prop it against the pot in a way where it can fall. Too-short cords have their own problems, including making it very hard to take the lid on or off sometimes.
If you do have the cord, it's important that the length be exactly right -- not too short and not too long.
The string can be useful in a couple of ways, though. One way is the way Cloud suggested, to identify different pots that look the same (no need to actually have the "leash" for this, though, just some knotwork around the handle). The other is to help out your fingers a bit (in terms of temperature).
I have one pot with the cord, but for the most part, I don't use it.