My T works from a communal clinic which is basically an apartment. She doesn't lock the therapy room and it's fine. There were rare occasions that people knocked/opened the door mid-session, NEVER her clients, just rude people waiting for another T and not realizing how inconsiderate they are.

I would actually hope not for a locked door as much as for a private place, I have ADD and sometimes people talk in the waiting room and it makes it hard for me to concentrate. I talked with her about this but she is adamant that this clinic's pros outweigh its cons so I let it go.