Aperture f/2.8 on the Fujifilm X100F is technically superior to f/2. The corners are not as soft. The center is sharper. Vignetting and chromatic aberrations are pretty much gone. But f/2.8 doesn’t contain nearly as much magic as f/2. Notice that I said “nearly as much” because some of that magic is still there. This aperture is both better and worse than shooting wide open on this camera, and overall not all that much different.
Perhaps the biggest reason to choose f/2.8 is for depth-of-field, which is shallow enough to achieve subject separation and large enough to have lots in focus, depending on how far away the subject is. Sometimes f/2 can be too shallow and f/4 not shallow enough, just depending on the situation. It’s a great choice for portraits or low-light situations. I appreciate the way it renders photographs in a variety of situations.