Without prototypes, the following two calls are equivalent: 
sub ratio_change {...}
my @args = ($start_value, $start_total, $new_value, $new_total);
ratio_change @args;   # Same result as:
ratio_change $start_value, $start_total, $new_value, $new_total;

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But with prototypes, they aren't: 
sub ratio_change ($$$$) {...}
my @args = ($start_value, $start_total, $new_value, $new_total);
ratio_change @args;   # Eeks. Won't do what you think it does.
ratio_change $start_value, $start_total, $new_value, $new_total;

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I don't shy away totally from using prototypes, but the only types I use are: 

sub foo ();
sub foo ($);
sub foo (&@);
sub foo (\@@);
sub foo (\%@);

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that is, I purely use prototypes to tell the parser how to parse things. I don't use it for argument checking (which is the typical use for '$$$$' style prototypes) as that get annoying fast - due to '$''s side effect of creating scalar context.
Perl --((8:>*

In reply to Re^3: warnings and strict -- The 2 Best Ways You Can Improve Your Programming by Perl Mouse
in thread warnings and strict -- The 2 Best Ways You Can Improve Your Programming by liverpole

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