For me, there are a couple of advantages, in particular situations.
When shooting through my microscope, the camera is shooting straight down into it, and it would be VERY difficult to look down through the viewfinder or even work with the live view on the back of the camera AND work the microscope, slides and light(s) PLUS all the camera controls, and that's especially true for stacking. Having the tablet as a display there on the table next to the microscope and having the camera controls right there on the tablet makes the setup as a whole MUCH easier to work with.
When shooting macros, I have a similar problem because I often need to be able to interact with the macro subject and it's lights, modifiers, background and so forth directly, especially during the setup and staging, and that's all set up in front of the camera. That means I'm often sitting in front of the camera as well, to the side of the macro staging area, where I can easily access that macro subject. Having the tablet facing me allows me to work with both the macro subject, lights etc., and still be able to see as I work with it what the composition looks like in a live view without going back and forth from that position next to the macro "stage" to the back of the camera, then back again to make another adjustment, then back to the camera to assess how that now looks, then back again, etc., etc., etc.
I can also zoom in on the tablet to 5x and 10x for precise focus and, indeed, the much larger screen works VERY well for that. Shooting in live view and lightly touching the tablet face to trip the shutter means I have no camera shake issues either. I can control ISO, aperture, shutter speed and nearly everything else I'd want to control from shot to shot right there on the tablet, without getting up from where I'm manipulating the staging area, and I can also work with the macro focusing rails as well as the geared head for precise movements having to do with composition and stacking with ease from that same position, all while seeing the effects right there on the tablet screen.
For portraits, I can easily show the client stills as we shoot them if I want to, without them getting up from where I have them posed, just by showing them the large tablet from my position or walking it over to them for a quick review - all without moving my camera at all and without them squinting at the small screen on the back of it. During setup, I can also have it face the posing area and move my lights and modifiers around and see the effects on screen as I do it, or I can take it with me via a long tether and hold it in my hand while making those modifications to see how they affect the composition.
With my long 30' tether, I can position the camera in one place, and monitor and shoot from somewhere else, up to 30 feet away. That comes in handy for skittish birds and so on. Just set up the camera on a tripod (and lights if you want) looking at the bait/staged area, get up to 30' away into a blind or the porch or have a seat behind some trees or bushes, and wait for the right moment to shoot while monitoring the live view on the tablet.
I can put the camera on the end of a pole up to 30 feet tall, clamp the tablet to the bottom of the pole where I can see it, and get shots from unique higher POVs while still retaining compositional control, rather than guessing I'm pointing it in the right direction, and still able to work ISO, aperture and shutter, white balance, etc., while the camera's up in the air.
I can use similar techniques to hang/boom the camera out over places that would be very difficult, dangerous or even impossible for me to physically get to and shoot from, and still retain full control.
I can use suction cups or clamps to position the camera on the outside of a vehicle, then monitor and shoot from inside that moving vehicle in the passenger seat because I have the live view on the tablet in my hands, and as always, I retain the ability to change ISO, aperture, shutter speed, white balance and more from right there on the tablet, and without having to pull over, get out, and adjust the settings on the camera, and hope they're right when we get rolling again.
Here's the bottom line: Using the tablet and the DSLR Controller app opens up MANY new possibilities for shooting, and the more I use it, the more uses I'm finding for it.