I don't have my best practices in front of me, but....
I don't believe that the tip is for performance, but more for readability and clarity. As a general rule, map is better when doing a transformation, for is better when doing an iteration.
Or more simply, use map when generating a result, use for otherwise.
-pete
"Worry is like a rocking chair. It gives you something to do, but it doesn't get you anywhere."