Questions like "What is the instrument used at 3:21 in this song?" are off-topic, because they are not useful to any future readers.
Today I saw the following question: Three days grace guitar distortion tone. It has a couple of answers and comments, and no close-votes, so I guess people think that this question is on-topic. I don't have a particular problem with this question per-se, but I would like to know why exactly we don't consider it as off-topic. To me, it seems like a "what is this effect?" question is quite similar to "what is this instrument?", and will rarely be useful to future visitors.