The SP theater is known for using real butter, hell yes, that's a major factor. It's not the closest to my house though, so I've only been there once or twice. If I'm not mistaken (unless there's another entrance I'm not aware of), you also have to do some trekking through the casino to get to the theater in South Point, which I try to avoid, if for no other reason than avoiding cigarette smoke.
I typically hit Green Valley Ranch casino for my nearest theater. Used to be Fiesta Henderson even closer, but it appears Fiesta may have closed not just for COVID, but closed for good. That would suck, I enjoyed going to the theater there. Sometimes I hit the Galaxy Theater, known for their luxury recliners and also real butter I think, some more food options, and even a decent alcohol selection (though I don't drink at the theater), but that's also not quite as close. Definitely a great place to watch movies though.