whether should I create autoreleasepool if I detach a new thread

Question

NSAutoreleasePool, as the document says, “if you detach a thread — you need to create your own autorelease pool.” Previously，I thought when detach a thread, it maybe cause memory leaks, but when I was testing, there was no leaks. So how to explain The document? Does it still need a autorelease pool? Can you help me? Thanks very much!