I find it therapeutic for anxiety, because when I'm kind of freaking out about something, and I write it out, it forces me to s-l-o-w down. Your thoughts will have to slow down to the pace of your writing.

Also, it is a bit like therapy, but not true therapy. I am sure we are all guilty of using our therapists as a sounding board/toxic waste dump, and this is a replacement of that. You have a place to 'put' your toxic thoughts, and kind of look at them objectively once they're outside of yourself.