IATSE membership helps with job mobility because they enjoy a carve-out allowing sectorial bargaining. It would be illegal in US for a union to try to organize the software industry along the same lines.
Wow, illegal you say? Damn, I suppose an organization that is capable of shutting down an entire sector of the economy will have to obey the strict letter of the law...unfortunate.
I was just trying to point out that the rules for entertainment industry are different than most industries, so IATSE may not be the best example.