As you might have guessed, a 400-megapixel image is substantially bigger than one of its 100-megapixel counterparts, with the former taking up as much as 200 megabytes when compressed into a JPEG file. The denser image is also more cumbersome and time-consuming to process in Photoshop and other image editing apps.
Obviously, no hobbyist needs a camera capable of snapping 400-megapixel images, and most professionals don’t need one either. But as Fujifilm points out, the feature does make a lot of sense for cultural preservation work where those images can help archivists and restorers go about their work. If you’re fancy enough to own a GFX100, you can download the new firmware from Fujifilm’s website.