I agree. You will probably spend twice as much time debugging, and later maintaining, your code then you will writing it (stolen from Perl Best Practices, or some book like that). So, it makes much more sense to optimize your code for later readability and ease of understanding (two or three months later when you don't have the whole thing in memory) then it does to optimize it for the initial ease of writing.
Of course, one line is always quicker to read then five, so if you're sure you'll be able to quickly understand that one line instantly, at a glance, months later, then that one line will be the way to go.
And that's the tradeoff, which will always evaluate differently for beginning, mid-level, and advanced Perl programmers.