It would be helpful if one of the mods could explain exactly what the frame and file size boundaries are and what if any image compression is used. It was once stated that there was ample storage available but this being a personal ad-free site I think everyone should be sensitive to keeping file sizes to a minimum. In the absence of automatic file compression that means all image files should be edited by the user with photo editing software or posted from a photo service that does automatic compression. No uploads directly from camera or camera phone unless the photo was taken using the smallest file size.
Personally, I shoot jpeg photos at the largest frame and file sizes that my cameras are capable of. This gives me ample room to crop and enhance the image for publication. For sharing by email or posting on the web I find that frame width of 1280 pixels and reducing file size from ~7mb to about 200-350kb works fine. At that it takes a lot of images to fill server storage.