"engines do serialize and strip out duplicated media-queries so they only need to evaluate each media query once. Also they cache the queries so that they can re-use it later on"
"In current implementations as of August 2012, no popular user agent pre-fetches resources that are subject to media queries until those media queries are satisfied. However, it seems like a more intelligent approach could be taken based on the liklihood that the media query may be satisfied at some point after a page has loaded. "
Media Query & Asset Downloading Results A little while back, I mentioned I was doing some research for the book about how images are downloaded when media queries are involved. via Pocket
"Does combining the media queries have any actual performance improvements? Are people simply raising issue because they don't like the way the output CSS looks? That's a damn good question and one that Aaron also raised. As he put it, "Let's ask science!""
"I did some research about how images are downloaded when media queries are involved. I wrote up some automated tests where Javascript could determine whether or not the image was requested. I've got enough data now to be able to go into detailed findings."