How does using "had" change the sentence meaning or grammar below - is it needed?
Jamie returned to the table to grab the plane Bill had folded for him while they were waiting for the food.
vs.
Jamie returned to the table to grab the plane Bill folded for him while they were waiting for the food.
(on a separate but maybe similar note: Is there a difference between saying "...the plane Bill had folded..." vs. "the plane that Bill had folded...")
Americans have no problems with any of those sentences, and prefer (of course) the second, a simpler one.
British people feel the difference, and use the first one, which is in the form of the past perfect simple tense, because the whole sentence is about the past, and one action (folding) was finished in the past before the other (returning, also in the past) was started.
To your second question, "...the plane Bill had folded..." vs. "the plane that Bill had folded...", both forms are correct but the first one is more often used because of its simplicity. The second one is used to emphasize who had folded it (Bill).
I'm not sure it changes the sentence at all. In both cases the bill was folded at a previous time. Leaving out had might allow you to think that Bill only folded the plane just as Jamie returned to get it. I think mentioning when he folded it tells that it was already folded when Jamie came back for it.
