It's pretty common for websites to offer a simple viewand an advanced viewfor data entry. Heck, even Google has an advanced search page.
This example would also require the server side to handle default values for the advanced view since those fields will be posted, even if they are hidden.
This little trick can save quite a bit of development time when applications require a simple and advanced view for data entry. It's not perfect, but it's quick and easy to implement. I think it would be really cool to use scriptaculous effects to smoothly display the advanced components instead of just magically showing up.