[wolf550e]

server push just means that when a server sees a request for index.html, it can serve index.html and also index.js and index.css without those being requested, and when your browser parses the html and discovers it needs the js and css, they are already in cache and are fresh enough to use, which saves the round trip latency and might enable a mobile radio to go to sleep earlier.

[0x0]

What if the browser already has those in the client cache? Will it have to abort the pushes, and will it even be able to do so in time on a high bandwidth high latency network like 3g/4g?

Is there a risk that cellular data usage will increase from this?

[dcsommer]

Yes there is. Knowing when a client has a resource cached already is an important part of server push. There is indeed a risk of over pushing.