I think it depends a lot on the type of practice. T's usually try to balance their caseloads so that they don't have more clients who may be expected to have crises than they can reasonably handle. Or they may be in a group practice where different colleagues cover.

My T had told me that one of the most important parts of his practice was working with clients to prevent crisis responses by building up skills and constancy. So, for example, giving me his home phone number and urging me to call if I were feeling in crisis would allow him to intervene and prevent its escalation. It's a judgement call. And boundaries are important, too, in order to reserve interventions for extreme circumstances only. That said, he had to implement boundaries differently in his University job vs his private practice because he was bound by University policies in some cases, whereas he had more latitude in his private practice.

I think in many cases it isn't so much the T's personal boundaries that dictate responses, especially the policy of referral in crisis, but insurance carriers controlling liability.