Every Perl project that I've been on hasn't had formal builds, because it's not a compiled language

I'd go along with everybody else and say it really doesn't matter that it's Perl. The important bit about regular builds (and personally, I think daily is the absolute minimum and I usually do it far more often than that) is that everything compiles, and all the acceptance and unit tests pass.

The good things that regular builds give you is feedback that you've not broken your product. Compiled code is just a byproduct.