I know that SG asks for photos in very high resolution but there is nothing more frustrating than clicking on a photo that looks stunning in miniture only to find out that someone has blown up a small photo to increase the number of pixels. This often means that the large photo is so grainy (film) or pixellated (digital) that it looks terrible. PLEASE DON'T DO THIS.
I tried to gently suggest this to one model recently but she got upset and told me that remarks like that should be sent to the photographer not the model. I don't have a very high opinion of any photographer who would do that. However I would also recommend that any model who takes pride in her work view her photos full sized as well as small before uploading them.
I also wish SG would just refuse to accept any photos where the quality isn't up to a certain standard.