They are really popular around here, and I don't get it either. Having done lots of roof repairs, I know that every one of those valleys is asking for trouble, and in my experience (I'm doing a repair, after all) is that the original roofer didn't use enough flashing or underlayment to keep the water contained. The valleys are also just asking to be clogged with debris. The photo that
@bcp posted could be any one of the newer homes around here.
I don't know if it was low skill, or cheapskate behavior, but I do see those valleys as a risk.
And I agree with
@4570Man about perforations in a roof, and the challenges of most metal roofs. Although I don't mind standing seam metal roofs, as the few that I have seen seem not to have the fastener and perforation challenges of other metal roofs, but I'm not an expert by any means.
All the best,
Peter