Many people prefer to view or read a story without having any clue as to what happens in it, or at least not much of a clue. Terry (Fhd remix 18:11, 17 June 2011 (CEST)) had the benefit of watching The Matrix in this way, and thus had no idea of the context of "The Matrix" until it became apparent in the movie. He did not have this benefit for The Terminator, and thus failed to recognize for years that an "unspoiled" viewer would probably have made the wrong assumption as to who was the "good" terminator and who was the "bad" terminator, thus the Recita Mall shootout would have been a major twist. This is what we mean by "spoiler".
The "worst" spoilers on this site and elsewhere are actually the fan fiction novels. The reason for this is because the world of Haibane Renmei is never given a context in the anime series (you're never given a date or how to find it on the map), and it is this lack of context that makes it so appealing to some of the fans. Many, if not most, Haibane Renmei fan fiction puts the world of this anime series on a map and timeline, (Terry could rattle the one off for FHD Remix right off the top of his head!) Wouldn't it be terrible if you couldn't see the original anime series if you "knew" where it was in the world? Its inherent innocence and beautiful naivete could be destroyed for you. That's why we have a spoiler warning.