Why do you update your post instead of answering to ikegami's reply? This makes it rather difficult to follow the discussion.

Also, a note about the undefined order of execution. The fact that some compilers seem to behave in a certain manner does not mean that you can rely on it. It means that they can change their mind whenever they want, without notice, and it's simply plain wrong to rely on it.

This said, it can probably be useful only in some golfing competition, where you can be sure that a certain version of perl (with the lowercase "p") on a certain architecture will be used, and you can thus take advantage of any implementation decision, feature or bug this perl exhibits. Usage in obfuscation is weaker, IMHO, because it could behave differently across different versions or architectures.