I'm really not sure how I can make this any clearer.
Take an example.
Let's say your rotation involves five different blocks of content.
When a visitor (or SE) loads the page, ONE block will be displayed. And ONLY one.
That means that visitor (or SE) will ONLY SEE that ONE block - they will NOT see the other FOUR.
So the EFFECT of your selective display is actually to HIDE four fiths of your content.
Several people have mentioned headlines, teasers, links, news items - all fine. YOU talked about revolving the actual page content.
You lose 80% of the time (assuming you display one in four ... what is your display ratio?).