If you happen to be working on testing your client side caching of things like images and JS files, you might be banging your head against a wall wondering why you are not seeing any HTTP 304s being sent while analyzing the network traffic with the IE F12.  Those tools apparently suppress the browsers ability to cache these files, most likely to aid people who are debugging javascript from trying to understand why their changes aren’t being seen.  If you look at the Fiddler image below, you can see I loaded a site, which resulted in mostly 304s.  I then opened F12 in IE and reloaded the same site, and from that point on it avoided its cache and downloaded all the files.