I don't have multi-quoting enabled because it makes it possible for (mistakenly) "replying" to content not being discussed and throwing the original topic of the thread they're replying to off course.
If the context of that quote is necessary to add to the conversation, they can easily copy the Reply BBCode over to their new message.
Reply is enabled so you can easily select/reply to individual sections in that thread, which keeps the topic on course.
I'll reverse course on my decision if members request it, though. I just see it as a more "glorified" Reply button as it allows you to grab from outside the current thread to reply to in the current thread, and one more option that can be confused for the purpose that Reply is intended for.