It is easy to forget the degree to which design-related choices made for a website can impact everything else - from user experience and conversion, and apparently to search engine optimization initiatives as well.
Website owners and 'Net professionals that have content placed in tabbed areas or through "click-to-expand" javascript features (a design/UX approach which is less intrusive overall) are struggling to get that content into the search index at Google. In a recent Webmaster Hangouts video with Google's John Mueller, the reason why is revealed.
Mueller, as seen in the video here (starting at 9:00), was asked how Google treated 'click-to-expand' and explained that Google feels it should make use of the content that is visible at the time of accessing the site as a user. This could mean that Google may discount information (essentially it is treated with less weight) hidden with tabbed areas, revealing that it could be confusing to a users coming from their search results if the content is not immediately available for them to see.