Sentence Correction

In conversational English, "that" can have several functions.

Consider: That bird is weird looking.

Here, "that" is a modifier stressing which bird we're talking about: the one right in front of us. The GMAT will almost never use this type of "that" in SC, because it requires outside context, which is rare in a single sentence.

It is possible to see this usage of that, though. Something like: The CEO proposed major renovations, but that idea was rejected by the board.

In this case, "that" wouldn't be a "warmup/middleman," because it's identifying a subject in an independent clause.

For the most part, though, you're right: the vast majority of the time when you see a "that" in SC, it will be introducing a subordinate clause that it modifying the main (independent) clause. More on that here: https://www.beatthegmat.com/sentence-cor ... tml#708709

Were there particular examples that you found confusing?