Perl is a "dynamic language", and generally encourages late, lazy, and dynamic programming.(Sorry - could not find a better introductory platitude)

Typically, built-in functions do not care (or are unaware) weather they are passed constants, or variables. The only exception I can think of is re-evaluating regular-expressions in a loop.

So the advice is to go ahead and feed in constructed arguments. Benchmark it, if you have doubts.