They're a significant indicator that you're reading a message from someone who doesn't mind inconveniencing an unknown number of people to gain a negligible benefit for themselves. :) Or, at least, this is what I remind myself when I catch myself using them. Typing is not a hardship. I spend time trying to come up with the absolute clearest way of writing what I'm trying to say, so why would I then take a step backwards (potentially) in clarity just to save myself three seconds of typing?