Bigger buffer, smaller filesize means less memory used, easier to compose the shots the way you'd actually like them at 17mp. There's several reasons I'm a big fan of having crop mode. I have it mapped to a button on the back of the camera so that I can quickly snap between 1.6x crop and full frame if my subject gets close enough for full frame to be useful.
A lot of times when I'm photographing wildlife or breaking news, you're just so far away from the subject that you'd be wasting quite literally dozens of gigabytes on empty space. It's a lot faster and easier when you're in crop mode to cull 2000 images of a distant subject at 17mp than have to hassle with 2,000 45mp images that only are using a small portion of the frame.
If we're talking about a 120mp camera, that's going to be a *serious* difference in filesize. That's easily saving hundreds of gigabytes of empty space and making the buffer far more usable, no matter what the buffer is.
Add to that, it's easier to find smaller subjects in the frame at 1.6x and easier to keep a focus point over a bigger subject in the viewfinder than trying to use even the spot focus point on a tiny subject.
It doesn't make sense for a lot of people to use, but for the times when a 1.6x crop camera makes sense to begin with, it definitely has its place. I personally enjoy the ability to use the camera as a full frame 45mp camera, and then in the instances when I need the reach, turn it into a 1.6x crop camera.