Rails - etags vs. page caching (file cache)

Question

What would be some advantages of using etags/stale?/fresh_when? instead of page caching (on a file cache)?

Apache automatically handles etags for static files, but even

Answer 1

Another use that occurred to me was that you could still process some information before letting Rails hand out the "304 Not Modified" header. Like if you want to record hits to a page.