In the first case, when temp() is called @_ contains ('Send'), while in the second case @_ contains ($obj). Since temp() doesn't use @_, that difference isn't significant here. However, if you have a method that needs to access instance data, you'd need to call the method on a specific instance, of course. For example:

package Send;
sub poke {
  my $self = shift;
  
  $self->{thingy} = 1;
}

sub new {
  return bless {}, $_[0];
}

package main;

my $obj = new Send;
$obj->poke();                # good

Send->poke();                # bad
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Really it just depends on what you want the method to do.