I have two years worth of voice-recorded sessions in a hidden folder on my computer. I have not told my therapist and see no reason to ever do so? It's legal in my state, it doesn't influence the way I interact with her and it hasn't affected her performance whatsoever.

I don't know how she would feel about me doing it without her knowledge.. not that I particularly care, either. It would be hilariously hypocritical of her to tell me I could not record our appointments, given that she has at least 192 days worth of notes with things I've said on them.