Well if you have an app or website that enables photosharing, you'd want to capture content from offsite and deliver it into your gallery.

Importing stuff from the big sites--Flickr, et al is great, but say someone has everything sitting on their personal webpage or scattered on site around the internet?

Instead of making them save, then re-upload a bookmarklet is great.

I'm working on an app that incorporates outgoing social media messages. If there is a link in the message I hit it on the backend and send a json list of image urls to the user. The user can then flip through them and decide which image to add to their message.