The home page cache gets old and stale.
50 visitors request the home page at the same exact time.
The server gets clogged running the exact same query for all 50 visitors.
Meanwhile more visitors hit other pages and nobody ever gets results because the server is overloaded; the dog-pile effect.
The home page cache gets old.
The 1st visitor triggers a database query to get fresh data. The other 49 get the now slightly stale data. Only 1 call has been made to the database.
The cache is updated with the fresh data that was sent to the 1st visitor and everyone is happy.
It's slightly more complicated but the results are already promising. Hopefully this keeps RSSmeme speedy.
A stale article, if you dip it in a good, warm, sunny smile, will go off better than a fresh one that you've scowled upon. see the link below for more info.