switch($number)
{
  case 6, 12, 13, 37, 44, 68 { \&subroutine(@args); }
  case 1, 29, 77, 98         { \&othersub(@args); }
  default                    { sleep(1); }
}
[download]

if(($number == 6) || ($number == 12) || ($number == 13) || ($number ==
+ 37) || ($number == 44) || ($number == 68))
  { \&subroutine(@args) }
elsif(($number == 1) || ($number == 29) || ($number == 77) || ($number
+ == 98))
  { \&othersub(@args); }
else
  { sleep(1); }
[download]

Now, the method i personally use atm is to create a hash(or in this example above I'd even have used an array because all the case values are numerical) that would look something like this(copied from actual code I use atm):

my %actions =
  (
  '001'     =>    \&_rpl_welcome,
  '005'     =>    \&_rpl_isupport,
  '332'     =>    \&_rpl_topic,
  '333'     =>    \&_rpl_topicdetails,
  '352'     =>    \&_rpl_whoreply,
  '353'     =>    \&_rpl_namreply,
  'JOIN'    =>    \&_msg_join,
  'PART'    =>    \&_msg_part,
  'KICK'    =>    \&_msg_part,
  'MODE'    =>    \&_msg_mode,
  'QUIT'    =>    \&_msg_quit,
  );

sub process
  {
  my($self, $line) = @_;
  my @text = split(/\s/, $line);
  if($actions{$text[1]})
    { return(&{$actions{$text[1]}}($self, $line, @text)); }
  }
[download]

why would we use switch instead of elsif?

I wouldn't.

And here's why: from the docs:

BUGS
There are undoubtedly serious bugs lurking somewhere in code this funky :-) Bug reports and other feedback are most welcome.

LIMITATIONS
Due to the heuristic nature of Switch.pm's source parsing, the presence of regexes specified with raw ?...? delimiters may cause mysterious errors. The workaround is to use m?...? instead.
Due to the way source filters work in Perl, you can't use Switch inside an string eval.
If your source file is longer then 1 million characters and you have a switch statement that crosses the 1 million (or 2 million, etc.) character boundary you will get mysterious errors. The workaround is to use smaller source files.

See also Re^4: How to use select (Switch.pm considered harmfull)

Now, now. We all have our little obsessions. What would life be like without them?

On a more serious vein (only slightly), switch statements, at least in some languages, have specialized behaviors (such as fall-through) that are not as easily replicated with a chain of if-statements. Also, a proper switch statement can make the code look a bit cleaner than the if-statement rendition of the same logic. Also, I imagine that compilers may be able to optimize a switch statement more easily than a chain of if-statements, but here I am definitely talking out of my hat.

I think ultimately it's largely a matter of preference. I haven't used a switch-like statement in years.

Why do we have unless when if not works as well? Why do we have for and foreach as they are exactly the same?

There is more than one way to do it!