I like that they've made it easy for us to keep track of our emails, as well as their responses.
Sometimes we have to remind ourselves that we're communicating with them via email instead of talking! It's sometimes hard to tell if there was an actual response or not when you don't hear back right away. Also, once someone has responded to one of your messages, how do you know which ones are going through? We can easily see who is responding to whom, but then how would we differentiate between those being responsive versus just reading what we write? This helps us keep up communication with our customers about how things go over at the company.