[Yunk]

You should look in webmaster tools if you want to understand how to use schema in SEO results. I've found things like Events are well supported and relatively easy to mark while things like product offers and reviews are more inclined to be ignored (or intermittently held to higher unpublished standards?) by google probably due to their high utility for abuse.

Personally, I mark everything I think is meaningful to a human and check that google thinks it is validly formed and how they would display it, but I don't rely on whether they do. With good and consistent metadata, Client side code+CSS can be a bit cleaner and better abstracted and it seems to help a little in the long tail of search engines/aggregators, etc.