Rather than confining, a boundary can be liberating.
For example. Each week this message runs about 150 words, plus or minus. Without such a boundary, these messages could become long and unwieldy, losing their focus. Forced brevity, while more difficult, is a far better taskmaster than your attention span.
Same in your practice. Having razor sharp edges identifying what is your responsibility and what is a patient's responsibility, grants you tremendous freedom. It helps you avoid taking certain patient choices or behaviors personally. It reduces the burdensome need to micro-manage patients. It gives you greater discretion to apply your energy and attention where they can have the most impact.
You must have clear boundaries if you wish to help more people. In under performing practices, it appears as if you can afford to meddle in the lives of patients. Busier practitioners know better. That's one reason they're so busy.