One thing it can be used for is for resizing a bunch of images, as such:
<img src="http://link/to/my/image1.jpg" original="1280px" />
<img src="http://link/to/my/image2.jpg" original="2000px" />
<img src="http://link/to/my/image3.jpg" original="1600px" />
.... and so on.
All those images are extremely big so I use jQuery to resize them back to about 700px. As a result, I also allow the user to click the image to resize to its original width... which requires me to somehow log the original width.
That's kind of why I want to know how to store data.... INCLUDING if it's something which has no innerHTML (or $.html()).