I like being able see who is not receiving my emails or how many people have opened it in order get an idea about what works best with sending out bulk messages without worrying if they got your message yet! None really as far us using this tool go but maybe be sure you know why its working well when there isn't much feedback coming back? Check our current open rate before making any changes so we don;t hurt anything important by fixing something wrong now instead later down stream after more testing etc..