While
printing sizes remain the same with different DPI settings, the images expressed in pixels change dramatically along with the overall file size
as seen on a monitor.
Example: Two of the same images with different DPI settings as seen in Photoshop:
300 DPI Image: 1728 x 1152 pixels. Print size: 5.764" x 3.833" (rounded off)
072 DPI Image: 415 x 276 pixels. Print size: 5.764" x 3.833" (not rounded off)
The fewer pixels, the lower the file size and thus less bandwidth is taken in uploading the image. If these were to be printed, they would be identical in physical dimensions, but not in image quality. Viewed on your monitor, seeing is believing. The lower the DPI setting, the smaller the image which conserves server space. More space on the server, the better its performance.
The good news: To my knowledge our host does not enforce such things. I just consider it a courtesy though, to resize the file density of very large bitmap images on general principle.
Even though the forum is set up only to upload compressed format files like jpg. Data compression helps, but you can still create some might huge files even in that format, depending on the level of compression one uses when saving a jpg file. And not everyone is necessarily aware of such considerations.