Even if you have 'unlimited' bandwidth available it is being paid for somewhere along the line.
It still makes sense from a users perspective for authors to ensure their materials work in the best way possible.
For example an image from that very nice 12MP camera you have is 4000 x 3000 pixels so you add it to a page and rescale it to 800 x 600 by just dragging in the edges. You now have a rescaled 12Mp image on your page when you publish it.
Your user is still using that bigger image, all you've done is have them load a 1.4Mb file and then rescale it on their PC, the file really only needed to be 114Kb.
Even if you have 'unlimited' bandwidth available it is being paid for somewhere along the line.
It still makes sense from a users perspective for authors to ensure their materials work in the best way possible.
For example an image from that very nice 12MP camera you have is 4000 x 3000 pixels so you add it to a page and rescale it to 800 x 600 by just dragging in the edges. You now have a rescaled 12Mp image on your page when you publish it.
Your user is still using that bigger image, all you've done is have them load a 1.4Mb file and then rescale it on their PC, the file really only needed to be 114Kb.