Some websites, like Wikipedia, use an
m. prefix to distinguish between the mobile and the desktop version. Mobile users often automatically get the mobile version when navigating to the desktop version, while desktop users usually don't automatically get switched when visiting the mobile version.
The mobile version is rarely designed for viewing on a desktop, leading to wasted screen real estate and visually less interesting articles. Some mobile versions even deliberately don't show certain content that is available on the desktop version (for example, the mobile version of wikipedia does not show the categories of an article).
I have no idea what the ratio is between mobile and desktop users is for the SE network, but even if we have more mobile than desktop users, I still think that, since mobile users often get redirected anyway when visiting a site, changing links from mobile versions of a site to desktop links is not exactly trivial. I certainly think they're as meaningful as spelling and grammar edits.