Keep in mind, “Sam is Typing” feature can be quite paralysing especially if there is no chat backchannel.
Unlike “Sam is Typing” that happens in chat, where people go: “Whatever I don’t care all white boxes must be filled with text” in forums you stop and think… ahhh Sam is already taking care of this so I might as well leave it alone.
But what if “Sam” thought the same about you, now stuff that may have gotten an answer will not.