If you want to do a self launch or landing,

the longer standard leash can be tethered to any solid object.

It is useful for solo riders, if the location or wind does not favor an unattached launch or landing.

Win

and it makes it easier to pass a kite to or from a friend or student, if the leash is long enough to safely/comfortably reach... (whether or not you think it would be safer to land the kite and then relaunch it, which it might in some conditions I guess.)