Here is the Wikipedia article about it.

https://en.m.wikipedia.org/wiki/Syndication_exclusivity

I can see the pros and cons of it if it ended. I would love to get a broadcast station from NY down here in Florida. On the other hand less than half of the broadcast stations show anything that stands out (like local sports), so if did end, I can hear people complain about a channel that is almost an exact duplicate of a local channel.

It still exists? Considering it seems every broadcast and cable channel airs "Big Bang Theory" and "Modern Family", rights holders aren't really using the regulation. Plus there aren't any superstations anymore, which were the main reason the regulation is passed.