The main application for leaf shutters is to allow outdoor portraiture with fill flash using less flash energy to light the subjects while in bright sunlight. 1/2000s flash synchronization means that the photographer needs three stops less flash energy than they would with a camera that can be used only at a top speed of 1/250s or 1/200s. This is a massive benefit. It basically mean the lights will weigh a fraction of what would be needed for similar results using cameras that support only slow sync speeds.
Right, so it's a camera you can use with lighter artificial lights when you do outdoor portraits in bright light. I am struggling to think of an important portrait taken under those conditions, but OK. If you have artificial lights, whether the pictures are physically within the studio or outside is really not relevant, they are still studio pictures. The question remains the same: why is it important what the camera weighs if you have artificial lights, because whatever they weigh, they weigh vastly more than the camera?
But sure, if outdoor-portraits-in-bright-light as a supplement to naked women being splashed with milk is your business, you need a lens with a leaf shutter. And you needed one several years ago, and if you didn't buy it then why would you buy it now? Because the second-hand market does not lie, and the second-hand market says leaf shutter lenses are not as much use as people thought they were.