"Speaking is always clumsy, while writing is always fluent."
If therapy can help someone, I would always prefer to speak with someone with the knowledge of thoughts. However, I prefer to write my thoughts, and this would just get us no where.
Writing your thoughts will always come out neat and perfect; you may erase or backspace, and any fumbling of your words can be fixed—just like that. Meanwhile, speech isn't so wonderfully done. The dialogue of any story can be messy, just the same way as speaking between yourself and a friend would sound. Your grammar is poor, your words can be miss placed, and sometimes, you might even use the wrong word at the wrong time.
This does not matter in general conversation. For one, conversations carry on in a way that allows the participants to know just what the other means, even when they cannot get the proper words out—or well, most of the time you should know what your speech partner is trying to say. It's all about the tone, the body language, and generally the way in which you speak.
In writing, since you can choose your words as you so wish to, the words will perfectly form into sentences, and eventually you can draft yourself a whole story. You know what you're trying to say, and you have the time to properly get it sorted out in your head before it all becomes the something you're trying to convey.
This is where writing to your therapist probably wouldn't work out.
Due to choosing your words carefully, the therapist can never work out what you're issues are since you're not really aware you're avoiding it. In speech, you can unconsciously give yourself away by your tone, stopping when you've reached something you didn't want to talk about, or generally the way you're face will scrunch up in discomfort or some other emotion that betrays you're inner feelings.
While I would love to continue my therapy sessions I had over this past semester of college through the summer, I know I cannot since the sessions would work better if I were face to face with my therapist. I love to write, and prefer it over face to face or phone conversations, I will never get anywhere talking to someone with carefully chosen word forms.
Sometimes I find that most of my problems in childhood (mostly from sixth grade on) stem from the fact that while I could talk to my friends just fine in instant messaging, I could not bring myself to speak aloud due to the fear of saying something that didn't make sense or generally embarrassing.
Writing what you mean is easy, but speaking the same way is hard...