if you're declaring 1 variable, its convoluted and a mess to do

my ($x)

my $x;
my $y;
my $z;
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but if you're instantiating a bunch of items before an eval block / loop:

my ( $x , $y , $z );

my (
     $x ,
     $y ,
     $z 
);
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both look cleaner to read and have a slighty faster perfomance (though its really insignficant). you can bench to see.

also: if you're doing oop perl:

sub function{
  my $self = @_;
}
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is bad form - what if an argument is missing/extra?

sub function{
  my ($self) = @_;
}
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is better. because you might want

sub function{
  my ($self , $arg1 , $arg2 ) = @_;
}
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