The reply-timer is not aimed at long discussions per-se, but to avoid quick-fire, heated back-and-forths between parties. The idea is that such exchanges are correlated with noise.
It's not relevant what it's intended to do, but what it does. If it makes long conversations hard, that's a con. (OTOH, if it avoids heated exchange, that's a pro. I don't really have a strong position one way or the other.)
