I think it's a habit and from what I've seen and experienced of it; I don't like the habit because the cursing has to take the place of "real" words that might actually communicate. Having to work to think of words, to try and communicate is always a good thing in my book.

I'd be startled by a therapist who swore. I guess only occasionally would catch my attention so I'd look at and think about what they were swearing at?