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Completely depends - though I agree, if you're going to do it, try and go beyond the obvious 'it's dynamic because it's light - outdoors! The bg is dark but the subjects aren't!' look. For your portrait, I think shooting a natural light would have been more appropriate and aesthetically pleasing. Then again, certain times call for strobe(s), and can really seperate your work and further your artistic vision; it really comes down to execution and really that is why so many are constantly pursuing that OCF mastery. In a few shots below, OCF actually makes outdoor, 'open' areas (like the girl in the door) look enclosed; when done correctly OCF can just give you more options then the 'strobist' dated look as mentioned above.
So, lot of blather to say it's situation and user dependant; with experience and style development, you learn more and more when is best to strobe (or not!)