Browsers make a best attempt at caching, but they dont have a lot of information to go on huge amounts of data that may be able to be cached and the only way to

Browsers make a best attempt at caching, but they dont have a lot of information to go on huge amounts of data that may be able to be cached and the only way to check if its out of date is by going over the network. Appcache / service workers give you more absolute control over that caching, generally once data is cached it is loaded immediately from disk forever thereafter (and updated in the background when needed).