I'll answer you in earnest, because I get why this is not intuitive.

Say you have 20 acres, and you want to split off an acre and sell it to someone else. But you don't want that "someone else" to be... I dunno, a pig farmer. (Because pig farms stink)

You can put a (reasonable, legal) restriction on the deed. "No pigs allowed." So even if someone buys that land, they cannot break that deed restriction and set up a pig farm.

If they do, it's off to court you go, where you will most assuredly win.