When you're walking your dog and want to stop somewhere for a few minutes to rest or chat with a neighbour, a carabiner makes it easy to secure a leash to a fencepost or bench leg.
Carabiners are useful for all kinds of things. They're also super light weight, so it's easy to clip one to the end of your dog's leash and just leave it there. If you need to stop and don't want to keep your hand on the leash, a quick clip of the carabiner secures the leash around pretty much anything. Sure, you could feed the leash through the handle loop and achieve the same effect, but that requires taking the leash off your dog first.
7 Carabiner Life Hacks [CrazyRussianHacker]