As a user example, when I load the HN front-page on an iOS device in portrait mode, I'm lazy and switch to rotate to landscape mode to see more without trimming edges and scrolling around. On most sites, I expect to be able to double-tap on a paragraph column to toggle maximize-fit-to-display-width mode and return regular all-content-on-display-width mode.
If some site prevents this, I will not buy their products or use their services, because it's a signal they don't care about usability and will inevitably waste people's time. That's a form of laziness and failure that should not be rewarded. There are usually competitors that want you to switch to their brand (except with govts). Those annoying jQuery Mobile one-sized-fits-all sites deployed by pharmacies, banks, govts and so on.