I know what you mean. I think there can be anxiety in waiting for the reply, it's in the therapist's hands and that can feel incredibly disempowering. There's something really important about knowing exactly what to expect and not feeling at the mercy of the therapist. It reinforces our autonomy. It's the exact reason I often write "don't reply" when I email my T. That way I remove the agonising wait which can reignite the shame cycle.