I've been in training programs as well and know a variety of ways this topic is handled. Some stress professionalism to the extent that it seems unreasonable and even not very humane. Along with that the emphasis on expertise and objectivity, which simply can't be upheld because this is not a science (and even in science it is not upheld strictly). This work is about subjectivity, the experiences of people, their take on things, their emotions. And that includes the therapist.

In the therapy I do, the therapist/analyst reads his own subjectivity, monitoring during and after sessions, to see how he is reacting. This is not only to make sure that he doesn't have issues; it is formative because his attunement leaves a mark inside him that he can use to understand the insides of the patient. The basic principle is not to correct behavior or even change things, but to get at the truth of subjective experience. That's where understanding comes in.

To put up barriers to this mostly empathic and affective process is to hinder the process. Being to rigid about rules and boundaries in the name of supposed professional can actually get in the way of being open enough to take in a client's reality and try to understand it.

Again I know what people are saying about disrespecting a therapist, and have already said so. But what I'm pointing out doesn't seem to be getting across so I'll try it again.

There just can't be absolute rules about this, no "across the board" except for sexual contact or exploitation. And therapists change with different clients. What they allow with one may change with another. It boils down to mutual respect, not rules. Rules are authoritarian and tempt people to break them. I guess you can say boundaries are equal to mutual respect but the word has connotations of walls, barriers, territory and is implicitly warding off not welcoming. Boundaries keep people out, not let people in.