This is simple. If you have hidden text and someone reports you, Google will wipe your site out of the index. Happened to a site a few years ago that I managed. My developer had created hidden div tags with content and didn't remove it. A competitor saw it in the source and reported the web site to Google. I only realized it after I was searching our keyword terms in front of my boss and our site was removed, gone. I was able to get the site back into the index only after pleading endlessly with Google. Don't do it...