substack/node-browserify — comment on commit 2d6b2120a34cb0331f3bd51e9cc41f68efda2879
File:  line 0
By bminer:

Yes, but if the user hits the refresh button, a request will be sent with the If-Modified-Since or If-None-Match headers. If the modified dates or E-tags match, then we can send a 304 Not Modified response instead of a more lengthy 200 OK response. So, both forms of caching are nice to have.