A lot of (news) websites provide at least short text previews (e.g., news articles) to search engines (e.g., Google). When browsing to such websites, those text pieces are not visible but replaced with a banner, e.g., "please subscribe and pay".
Of course, it is possible to hide/cover texts with CSS but then the information can still be found in the source code. Also distinguishing user-agents is not really secure. I checked both techniques on multiple websites and they seem to use another mechanism.
How to provide texts to search engine crawlers but not ordinary browsers?
