Currently double clicking does nothing. While there certainly are those who don't use Photoshop, there are a lot of us who do.
Taking advantage of the simple and standard interface of double clicking on a thumbnail seems a useful tool. I go back and forth to Ps a lot, and going through the process of right clicking and selecting a menu, while not difficult would be simplified with a easy double click.
I'm not sure if there are other functions that could take advantage of a double click, but I know I find many people in classes I teach are surprised they can't just double click to get to photoshop from the flimstrip. Certainly those that don't need it don't have to use it.
I find myself double clicking a couple of times a week. Just habit of "opening" a document.
No big deal, just curious