You asked

What is the fujifilm xf 14mm f 2 8 r good for?

Here is what the site says about that.

From Fujifilm XF 14mm f/2.8 R: Fujifilm XF 14mm f/2.8 R: A prime lens by Fujifilm for APS-C cameras, 14mm f/2.8. A sharp, low-distortion wide prime with a clutch for manual focus. Specs - Maker: Fujifilm - Focal length: 14mm (prime) - Maximum aperture: f/2.8 - Made for: APS-C sensors - Mounts: Fujifilm X - Stabilised: no - Autofocus: yes What it frames like - On APS-C (Fujifilm X): like 21mm on full frame; f/2.8 gives about the depth of field ...

From Focal length converter: Aperture and depth of field: The f-number sets exposure, and that doesn't change with sensor size: f/2.8 gives the same brightness on a phone as on medium format. Depth of field does change. At the same framing, multiply the f-number by the crop factor to get the full-frame aperture with the same depth of field: f/1.8 on APS-C gives about the background blur of f/2.7 on full frame, and f/1.8 on Micro Four Thirds about ...

Quoted from this site's pages.

From these pages