Why is three-argument open calls with autovivified filehandles a Perl best practice?

Question

I\'ve got two questions about the Perl open function:

1) I seem to remember from Perl Best Practices that the 3-argument version of open<

Answer 1

Tackling #2:

OUT is a global filehandle and using it exposes you to insidious bugs like this:

sub doSomething {
  my ($input) = @_;
  # let's compare $input to something we read from another file
  open(F, "<", $anotherFile);
  @F = ; 
  close F;
  &do_some_comparison($input, @F);
}

open(F, "<", $myfile);
while () {
    &doSomething($_);   # do'h -- just closed the F filehandle
}
close F;