There can be a problems with this, especially with tele/web-based/distance therapy. The resources to intervene within a crisis environment do not exist. For example, if someone is suicidal or homicidal, how does one intervene appropriately? What if a patient/client in a tough situation (ie divorice) and their coping skills are less than adequate, and they just terminate the session after stating "they hate their spouse. There is no way to ensure that the patient is safe. Even a 911 call to the police for a wellness check, the 10-12 minute response time is not immediate enough for crisis intervention. This could potentially setup any therapist using this type of session to have there A$$ sued off, even more than they already are.
Certain patients/clients would be appropriate for this type of delivery for therapy - Any of the various paranoid flavored diagnoses would likely not work well (after all, we all used to be called paranoid when we thought the NSA was tracking our internet usage eh?). Border-line personality disorder are extremely difficult to work with in the first place... they can go from I love you, to I hate you in seconds - try and deal with that over the web, when their first instinct will be to disconnect the session. Leaves the therapist in an extremely vulnerable situation.
The other issue is, as a therapist, you don't have control over the environment. What about the phone ringing during a session, or the young child that constantly wants to see mommie or daddy or the or the interruptions from the over-caffeinated teenager? Often people in therapy are lacking in coping skills and/or boundaries. That is where the office visit will be superior, because those boundaries are more clearly defined.
The security/confidentiality/privacy of sessions would be extremely difficult to keep under control. Most relevant code of ethics have specific rules (and not to mention federal and state regulations) regarding this. If you are cross-state, which laws apply? Those of the therapist, those of the patient, or a blending of the two? In this regard, the duty/responsibility generally falls onto the therapist - talk about a liability nightmare.
I'm not saying this method of delivery is not completely without value... there are circumstance that make it necessary or even desirable. Long distance, and/or limited access to mental health services, those that are constantly traveling for work, etc. would be some examples. In my own practice, this method of delivery would only be used in limited and very specific circumstances.