Google’s Matt Cutts On Hidden Text Using Expandable Sections: “You’ll Be In Good Shape”
Use of expandable content sections is very popular across the Web and used by large e-commerce sites and content sites to make the content on the page less threatening and more welcoming.
Matt said there are very good reasons to implement expandable content sections, but if you are doing it with the intent of tricking Google by hiding content, in that case it would be against their guidelines. Otherwise, “you’ll be in good shape” using this Web design technique.
The example Matt gives is how Wikipedia collapses some of the content on their mobile interface, here is a screen shot:
As you can see, for a page with a lot of content, this can be very helpful for users.
Below is the video:
Again, if you do this without the intent of hiding content from Google, you should be okay.