Here's something to read: Far More Than Everything You've Ever Wanted to Know about Prototypes in Perl.

I try not to use it in Perl partly because it gives you the false impression of security. While it enforces certain context/number of arguments, for some reason a lot of people I know tend to not validate their input if you have a function prototype. Which is really bad, especially when you try to make the transition from procedural to OO Perl, where no prototype check is done.

Plus it's really damn annoying when something like this compiles:

   sub foo($) {
     ...
   }
   foo(@bar); # = foo( scalar( @bar ) ). argh.
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I'd rather stick with Params::Validate