At its heart, all design is about communication, but the simple fact is that you cannot communicate anything if you have not gotten the other person's attention. Other elements of design may grab your attention, but typography will hold it.
Why typography matters
I can try to be the best writer I could be. I will try to hold your attention for as long as I can. But words can only go so far.
In many way , there has never been a harder time to be a writer. People's attention span's have not changed. There just happens to be a lot more distractions than there used to be.
Bad typography really doesn't help. If you want to lose your reader's attention the last thing you need to be doing is exhausting them.
There are the obviously terrible choices, like Comic Sans or Lobster. But those are just awful typefaces. Bad typography is a lot more insidious.