after reading about how he gets this look, I don't enjoy it. same with The Witcher; yes, it looks attractive, but all I can think about is Henry Cavill talking about how when you're that dehydrated you can smell water from a distance
Yeah the whole "dehydrate the fuck out of yourself to make your muscles pop a bit" thing is so irresponsible. Jackman pulled the same thing for the opening prisoner scene in the Les Miserables movie, which was doubly irresponsible because he had to sing, and being dehydrated makes it really difficult to sing well, and potentially puts you at risk to damage your voice. I think I've seen interviews where they spent like several hours on that scene because his voice kept breaking. So not only was it super bad for Jackman, it also wasted the rest of the cast and crew's time.
I don't think that it was him who decided that it was necessary for the scene, though he might not have been against it. Production would not agree to loose money on multiple takes if they did not want the Jackman abs.
Edit: I agree that it's a completely irresponsible practice though!