There are pros and cons to which way you go with this setting. The default setting ensures that the data in hidden form fields like __VIEWSTATE is available early in the browser-side page loading cycle, so that if a user clicks a button and posts back the page before it has fully rendered/loaded, the server will still get the contents of these hidden fields. This is a good thing, as otherwise the server will likely be unable to process the page. On the other hand, there’s a good argument to be made that search engines tend to weight content higher based on how close to the top of the page it is, and that in some cases search engine bots may only grab a relatively small chunk of a page (from the top) as part of their indexing process. Assuming there is some truth to this, then pushing real page content as high up in the actual HTML as possible would tend to yield better placements in search engines. Thus, setting this so that hidden fields render at the bottom of the page could make a big difference in how close the page’s real content is to the top of the HTML file, especially if there is a great deal of viewstate on the page.