Hmmm. This is a good one. I remember seeing, I think, a MADD PSA on TV back in the middle 1980s about this subject. They showed a teenage girl signing a 'Pledge' card with her parents; vowing to not ever drink and drive, and that she would call them should she ever be at a party where she had too much to drink.
I honestly don't know if I could have this type of arrangement with daughter. Of course, I'd implore her to call me whenever she was in trouble, I'd be there for her as far as I could; but 'No questions asked' would be pushing it. If she found herself in a situation that was so overwhelming that when I got there she was in hysterics, I wouldn't berate her right then; but you can best believe that once the situation calmed down, I would want an explanation.
The bottom line that I drum into her head is that I'm always available for her; no matter how awful the scenario is, she can depend on me. I understand and respect that kids screw up, and that sometimes parents need to dial back the indignation in situations that can be tucked away as 'learning experiences,' but my reaction would be based largely on the scenario. Maybe I won't blow up, and will just quietly allow her to ponder the choices she made that led her to that consequence, but maybe not. It really depends.
But, again, the bottom line is that I'm always available.