while im sure it gets mentioned on the page, simply reducing the ppi resolution (ie, 72 pixels per inch), doesn't change anything. It's changing the actual image size that matters. If you have an image that is say 2000x1250 pixels in size, at a ppi of 300 pixels per inch, changing the latter to 72 ppi doesn't actually alter the file itself, just the way it is displayed. It will still be 2000x1250, and thus, have the exact same amount of detail as it did before.