I don't know how to measure memory using or fragmentation by a single variable from a Perl program... I don't know even if it's possible. Again, the tip was about running the program faster, not to help to save memory.

Of course, I agree it may be a premature optimization. As you said, this is not a silver bullet... it may work, it may not. It's up to the programmer to put this to a test, but for sure there are more important modifications to implement first.