Highest rated segments - Question

I was wondering how highest rated segments were working.

For example, on NXT this week, Dom was the highest rated segment. But how does it work ? Do people know in advance that Dom is going to be on at that precise time so they tune in just for that ?

I’ve always wondered this. How do people tune in when say Cody arrives on Raw? My only guess was that it’s related to Twitter in some way. People are following on Twitter when they read about Cody, they tune in.

That would make sense.