The movie was so bad that it was hilarious.
The area was so cold that plants couldn't be grown.
The jewel was so expensive that people couldn't buy it.
In sentences like these, that is used to indicate result, but a result is "a thing that is caused or produced by something else" which would imply that at some point, the thing was not the thing indicated by "that." That means at some point, the movie wasn't hilarious, that plants could be grown, and that people could buy the jewel, but that doesn't seem right, but if "that" doesn't indicate result in these sentences, I'm not sure how else to define it.