... where you have to use a code block, and return the new array, just use "my" and not "our" appears to be the take away.

The preference of a lexical (my) variable over a package-global (our) variable has nothing to do with accessing a value generated within a code block (or lexical scope, as I would express it). The code in the OP using a package-global to return the values produced in the for-loop scope works just fine as far as it goes. The problem is that you are then left with a global variable. As the old punchline goes, now you've got two problems.

Global variables are officially Frowned Upon because they are... well, global: they can be accessed from anywhere in your program and can be the source of "spooky action at a distance" problems, potentially very tricky to debug. Lexical variables have a well-defined and potentially extremely limited scope (the more limited, the better), and can (usually) be reasoned about and debugged more easily. Don't give yourself headaches.