It's astonishing how much "responsive design" gets thrown around as a buzzword...however, unlike a lot of buzzwords, "responsive design" actually means something and implementing it has implications systemwide...Across legacy sites, I've almost never seen it implemented in a way that didn't hide critical information, often because the designers and the people in charge of the legacy CMS probably don't coordinate enough. Things like, "Make everything that isn't in a p or image tag go to the bottom of the page" can hugely affect the context of certain elements.

For example, I worked on a site that hand hand-coded captions for photos and so those captions ended up having tags that were displayed:none when the device had a low-enough width. That's not great for photos that require the context of the captions.